Wrong way round. She was born in the UK and was a British Citizen at birth and had a British passport

She is (maybe) entitled to Bangladeshi citizenship which is why the UK government was allowed under UK law to remove her British citizenship because British courts didn't consider her to be stateless.

The only people who can't have British citizenship removed are British citizens with no other citizenship or entitlement to a citizenship. I think in theory that means the British government is legally allowed to remove citizenship from any person from Northern Ireland if they justify it (since they're allowed to claim Irish citizenship under the Good Friday agreement).

At birth she was entitled to citizenship but she wasn't a citizen. Like my cousins. I describe the nuance in my other comments on this thread.