Nicely done! I rehabbed a blind turtle two years ago. It was slow going, and I thought for sure that I'd have to euthanize her if she didn't regain her sight. She'd been struck by a vehicle directly on her snout...crushed her head...AMAZING she survived!
1. Can she live a long life in captivity? - YES!
2. Vet suggested astroturf to line the terrarium. OK? - It depends on the species of box turtle (humidity related). Sure, it can be used if you can maintain the proper humidity. Make sure it has a very tough nap because I've seen some that are very delicate and the turtles will inadvertently ingest some. Also, make sure she has some places where she can snuggle in and hide. It may stress her out to constantly be on an open field of astroturf. Having said all of that...I personally don't think that astroturf is your best choice.
3. She appears to have very good hearing. Would she be smart enough to come to my voice? - YES! However, it may take up to a few years. As this is now one of your turtle's primary stimuli, maybe she'll respond faster.
4. I'm concerned that she doesnt move around much. I put her in a good basking location, I put her on her feeding tray, I place her in her shallow pool of water, etc. She can walk. - This same exact thing happened to me. I believe that it has to do with their confidence. I did exactly what you are doing...moved the turtle where she needed to be. Before long, she began to learn her way around the enclosure and did this on her own. One suggestion...once you set up the floor plan, don't change it.
5. Very concerned about what humidity I should try to maintain. - We'd have to know which type of box turtle you're dealing with. In general, ornates do well at an ambient AIR humidity of 50%-60%. Easterns do better closer to 75%. It's very important, though, to provide both Easterns and Ornates with a humidified substrate in which to burrow, and regular soaks in a decent depth of water. Humidity can be a real pill. It's best if they can get somewhat of a variety. For this turtle, you'll have to make certain to move her about in the enclosure so that she gets to spend time under the UV lights basking in "dry heat", then time hiding in her humidified substrate.
Good luck with this girl! Having gone through this, I know how difficult and time consuming it can be. My turtle was adopted out through my WRC and a turtle rescue team. Apparently, she's now as healthy, hearty, and active as a fully functioning turtle. They also said that she's bonded to them much more than their other turtles. They're assuming that it's due to the fact that she's so reliant on them.