You can do drills for this on the floor or floor bar as well. Standing in a pike with her hands on the floor/floor bar, jump to straddle, and then jump so her feet are a little bit off the ground in a straddle. Then go straight from pike to straddle in the air. Keep the feet not very far off the ground so she's not worrying about height, just making sure to feel that her legs are pushing all the way straight. Eventually she can try to jump all the way to handstand.
Another thing that is great for this is spotted straddle cast handstands with a coach (obviously not something you can do on your own) but it can help to eliminate things like fears and the desire to compromise form to get all the way up since the coach is helping a bit.