You’ve acknowledged but skipped over the key point there - possibly accidentally, possibly deliberately - she is entitled to Bangladeshi citizenship, she just has to apply for it, so she is wilfully stateless at this point.A UK tribunal accepted arguments by UK lawyers that she had Bangladeshi citizenship before turning 21, but ultimately the only authority on who is and isn’t a Bangladeshi citizen is the government and courts of Bangladesh and they have been unequivocal that you have the right to Bengali citizenship if your parent is born there, you don’t automatically have the citizenship.
Of course, she doesn’t want Bangladeshi citizenship as they’ve made clear she will be tried for her alleged crimes and executed if/when found guilty.
Instead she is now applying for Dutch citizenship by marriage, which she is not entitled to but is pursuing as it’s her only route now out of Syria that wouldn’t see her face capital punishment if found guilty of her alleged crimes.