(Apologies in advance for my excessively long post)
An easy hike would be northwest out of Falls Village on the AT to Giant's Thumb and then back to the meadow that looks northwest at Lions Head and Bear. That should be a great spot for picnic with views.
Here it is on a cold, overcast day in April. You can usually park up on Housatonic River Rd, by the falls, at the trailhead and skip the road walk from the power plant on Water St, although that's kind of fun too, across the old bridge.
I'll second this. It takes you over Mt. Prospect, but it's dead easy. 3.5 miles or so IIRC.
I've done this many times in the evening and have never run into more than one other person. It seems to be known more to locals and AT hikers than the general public.
I'd also actually park at the power station.
It adds a road walk, but I find it really pleasant. I almost always park there rather than at the falls. If your girlfriend is not from New England, she might enjoy the brief stroll through an NE village.
As you said in the OP, Lion's Head can be crowded. If you're willing to have a picnic dinner, you may have better luck--it's always deserted at sunrise and sunset (unless you run into me, but I wouldn't have a problem clearing out.
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There's also a secondary viewpoint on Lion's Head that is often overlooked. Continue north on the AT for a couple hundred yards. It's not quite as nice, but it faces north and the "leaf peepers" don't seem to go that far. There's a rocky area that would allow you to get a bit off the trail as well.
Other possibilities:
Caleb's Peak
Very easy and only a mile or two. Has a nice outlook of the Housatonic and is just outside of Kent. The summit is very small and I've only done it a couple times, but I've only ever run into a handful thru hikers. It's quite easy. I doubt it gets much traffic due to the more popular mountains around it, but I may be wrong.
Pine Knob
Easy loop with a nice view and interesting waterfall. Right off US-7 near Cornwall Bridge. Popular with the locals, but I've never noticed a crowd. There's a "main" viewpoint less than a mile from the trailhead (which actually consists of several ledges--unless it's absolutely packed, you should be able to find a spot,) but there's also a second one further south along the trail. It's not quite as nice, but it's a good hangout and I've always been alone at it even in the middle of the afternoon.
If you're willing to look outside of CT, the immediate area has a lot more to offer. All of these suggestions are within 20 minutes (mostly less) of Lion's Head:
Mt. Brace
Actually just over the NY border, but can easily be reached from trailheads in CT, MA, or NY. I'd recommend going from the NY side as the CT trailhead involves some minor scrambling and crossing two other mountains (Round and Frissel.) I don't know the mileage from the NY side as I've never done it, but it can't be more than 3 and is probably closer to 2.
The summit of Brace is basically a big meadow that offers a 360 degree view. I find it's always deserted in late afternoon or evening. Absolutely worth a look.
Jug End
A bit steep in places, but plenty of switchbacks. It has a rocky ledge that looks east and seems to be of absolutely no interest to anybody but thru hikers and me.
It can be reached from MA-41 at the AT trail crossing. You can also approach it from further in (a dirt road provides parking,) but I recommend going in from 41 since it includes a ~.5 mile walk through some of the nicest forest in the area. I'd say the total is about 3 miles, perhaps a bit less.
Alander Mtn.
Pretty easy climb, though it can be muddy in places. About 3 miles (I think--it has been a while. It's not very far or steep at any rate.) The summit features an incredibly creepy cabin that looks like it will fall down any day now and panoramic views towards both the eastern ridge of the Southern Taconics and the eastern escarpment of the Catskills across the valley. Several (pleasant) river crossings are en route. It does not seem to be a popular mountain for some reason, but the summit is long and mostly bare and you shouldn't have much trouble finding a place to yourself even if people are up there.
Parking is available at the forest HQ on Mt. Washington Rd.
Mt. Race (via the Race Brook falls trail)
This is the iffiest one I'm suggesting, but I figured I'd include it anyway. It's a little too much vertical to call "easy" (~2k or so total,) but it's still not overly difficult. If you've climbed Bear Mtn from Rt-41, I'd say that Race is slightly more taxing as a comparison. It's 3-3.5 miles one way, I think. On the way up, you will pass some of the most impressive falls in the area. Like Alander, Race's summit is long and rocky--you should have no problem finding your own place, but I've never run into more than a couple of people up there.
Parking for the trail is at a pull of on MA-41. It's on the left (heading N) a couple of miles beyond the Bear lot. It's a big semi-circle, so you shouldn't miss it.
If you're willing to forego a big view, I'd suggest a trip into Sages Ravine. I've done most of the AT in CT, and I think it's without question the nicest part, and the best part is that it doesn't see a lot of traffic. Lots of waterfalls and hemlock down there. Plenty of rocks and ledges that you could sit on, too. All in all, a beautiful spot.
To reach it, there are two ways:
1: Park at the Bear Mtn lot on Rt-41. Follow the trail to the Paradise Lane junction. Follow that to meet the AT at the head of the ravine.
(this bypasses the need to climb over Bear's summit--Paradise lane goes around it and saves quite a bit of vertical)
2: Park on the MA side of the CT state line on Mt. Washington road (3 cars can fit into the lot. It's unmarked, but it's pretty obvious. You can literally see the stone marker for the state line from the lot.) You'll have to follow the road south a bit, but there's an unmarked "trail" on the left that leads back to the AT and merges with it near the summit of Bear. You can then follow the AT to Race from there, passing through Sages Ravine. It will be longer (I'll guestimate about 4.5 miles, but I've never measured it,) but there will be less vertical. It's all pretty gentle except for the decent from Bear.
Option 2 is a bit more direct and features little vertical on the way in, but to get back you'll have to climb over Bear's summit. However, you still get to bypass at least 50% of the climb by coming in from Mt. Washington Rd.
Option 1 has a little bit of sustained vertical at the beginning, but probably has considerably less overall. Paradise Lane literally ends right in the ravine, so there's very little vertical on the return trip.
And finally...
Bash Bish Falls might also be worth a viewing: Not secluded (parking is right in front of the falls,) but definitely something worth stopping at if you're in the area. They can be reached from Mt. Washington road. Heading south, there's a sign on the right before the pavement ends. IIRC, it's the biggest waterfall in MA (by single drop.)
Here are some of my "visual aids" the area. I actually have shots for everything I mentioned, but not all are handy at the moment.
Lion Head's "main" outlook
Lion Head's "north" outlook
North view from Brace
Pine Knob's "main" outlook
View from Alander
(point of interest: That's Mt. Greylock on the horizon. You can actually spot it from quite a few South Taconic peaks if it's clear enough.)
Mt. Prospect view from last winter
(for referance, Jug End is the last summit on the ridge. Race is the leftmost of the two highest summits)
And a terrible view from Mt. Plantain
Mt. Plantain is a bushwhack that has probably been climbed a total of 3 times by non-surveyors, but it's just one peak over from Race and is the only thing I have handy that approximates the view you'd get from it (minus the trees, of course.)
Hopefully that wasn't information overload, but we're talking about my oldest stomping ground.
If you want any further details, feel free to PM me.
