Some skaters never achieve that spin position, so be aware of that. Her core must be solid and strong.
Do a youtube search and there are many coaches, trainers and more that offer videos that guide through stretches for more easily achieving this position.
I'd offer more help than that, but I can't type it all out so that you can picture what needs to be safely done, plus it would take forever.
Obviously a Biellmann requires a very strong back and core (many think it's just about splits). It's super important to be warmed up before doing any movements with extreme back flexibility.
You didn't say how long your skater was working on it......it isn't something you can usually learn super quickly (although I'm sure there are exceptions). I know skaters that have been working on getting a passable Biellman for years. it can take a long time and as Ic3Rabbit indicated, not everyone is even capable (my skater can barely do swan.....Biellman would be unrealistic). If your skater doesn't have the flexibility and strength foundation already, it will take some time to build that up first. Can your skater work on other stuff leading up to Biellman, like haircutter? Maybe try to learn haircutter first...