OK, if it's green she likes, Northstar and Squaw probably have it over the others, with Squaw out ahead.
For Squaw, go to the map at http://winter.squaw.com/html/mtnmap_upper.html
and check out East Broadway, Belmont, Bailey's Beach and Links. That's a lot of truly green terrain, all above 8000 feet -- much higher than any other greens I know of around Tahoe. I have never seen them crowded. Usually, they are empty. And they are surrounded -- in every direction -- by intermediate to expert terrain.
Mountain Run is also green, and it goes a long, long way. It is always crowded, though, and usually in poor condition by afternoon.
Unfortunately, the Northstar folks haven't figured out how to put a readable trail map on the web. What they have is at http://www.skinorthstar.com/winter/mountain/trailmap/.
The long green run that your wife might enjoy is the one along the gondola line, below all the other runs. Hard to tell from this map, but it is quite long for a green run. It's at least a thousand feet (probably two) lower than the ones at Squaw, though; and if it's not a very cold day, it gets pretty soft in the afternoon.
On this map, the run appears to extend up above the gondola to the top of the mountain. It's really two runs. The one above the gondola is a bottleneck that gets heavy traffic, including many young boarders with lots of speed and little control. Not a fun or safe place to be.
It always pleases me when my expert friends "dis" Northstar. I figure that rap explains why there's never a lift line to speak of on the back (all black) side. No cliffs, no chutes, no bowls, but it's really fun back there. Trees, trees, trees.
Now, if all goes well, and your wife gets interested in easy blues, go to Alpine. Except for Alpine Bowl, the blues straight above the lodge are all easy unless they've gotten bumpy, which will be obvious soon enough to steer clear.