Another, simple thing, you can do at home, is have her sit on your couch, or a long chair, etc... have her. Help her lean backwards so her hands are on the floor, and her back is arched with her hips elevated.
From there, she can work on walking over on her own. Start with a spot, make sure one leg at a time goes over, directly over her body (not around the side). The more she is able to do on her own, the stronger her stomach will get and the stronger her arms will get, to support the movement.
When that is too easy, have her do a bridge with her feet on a slightly elevated surface (like a sturdy stool, or even a low coffee table... if youre in a bind, you could probably come up with some creative ideas, or just use the wedge that you have).
Make sure when she is going for the walkover motion, her chest is "rolling" over her hands.
However - one thing I would like to point out... as much fun as it is to help young gymnasts get better - you may find in the long run to let coaching be done by coaches, and not take it home. If they work on stuff at home it's GREAT! But, home should really be a safe haven where kids can relax, especially if they become serious about competing. The last thing you want is to enforce a gym policy at home.. this can cause burn out really really quick.
Moral of the story is.. if you do these things at home, my suggestion is to present it as fun time or a game... not as gymnastics stuff. Try "something fun!" not "hey this can help with your back walk over" ... again.. depending on how old she is too...