I assume the grounds for her appeal being rejected was because at the age of 19 when she was stripped of her British citizenship she at that point automatically held Bangladeshi citizenship through her parents. So she wasn't truly made stateless which is what is illegal. I'm sure I read this morning that for Bangladeshi citizenship you have to basically say you want it by the time you're 21 otherwise you lose it. She never applied for it, so has effectively forced herself to become stateless.
Only the legal experts will be able to determine if that is all correct and if by forcing herself to become stateless whether that reverts back to being a UK problem.
All that aside, I appreciate the "camp" she's currently in isn't providing any sort of nice life, but she does have her freedom. She must realise that by returning they're not just going to give her a slap on the wrist, they'll throw the full book at her. Terrorism alone would be 14-25 years, no idea what other crimes have been committed but she could easily be looking at 20+ years of jail time.