Well, kinda off topic, but Jasper could still not be mentally cured. She'd still have the same grudge against the Crystal Gems about what happened with Pink Diamond. You can heal someone's wounds on the outside, but the healing on the inside is from the person itself, with the help of his or her friends.
Jasper doesn't have friends. The closest gem that she might have been friends with would have been Pink Diamond or some higher authority. Either way, it would take her some time to realize that Steven and the others aren't her enemies, and maybe a bit more to realize that life isn't so bad on earth.
That, or maybe Steven could just bubble Jasper as she starts to heal on the outside to see what the world on earth is like. Maybe Peridot will convince her it's not so bad if she'd stop looking at all the things that happened on it.
Maybe, she could become a Crystal Gem. I read somewhere around here that Sugar did confirm Jasper getting a redemption role in the 5th season.