I think the law says that one cannot make a person stateless. When she had her UK citizenship removed she became stateless, she was not a Bangladeshi citizen. She might be entitled to apply for Bangladeshi citizenship, but that does not alter the fact she is currently stateless. Bangladesh is no longer a colony and UK courts cannot interpret Bangladeshi law and say she is a Bangladeshi citizen. That is a decision for the Bangladeshi courts. The UK could bring a case in the Bangladeshi courts to argue that the Bangladeshi government must recognise her citizenship. However currently the Bangladesh government says she is not a Bangladeshi citizen.
This does stink of racism and neo-colonialism.
She was automatically a Bangladeshi citizen. I have linked the relevant law twice now. She doesn't need to apply. Bangladesh is breaking their own laws. The UK is following the law.
At the time the UK revoked her citizenship, She, under Bangladeshi law, wasn't stateless. Claiming racism is kinda silly.