Two politicians have said yes, because her British nationality cannot be eliminated as long as she doesn't take another nationality.
In fact, this is not true.
https://en.wikipedia.org/wiki/StatelessnessIn January 2014, the Immigration Bill 2013–14 was introduced to extend the powers of the Home Secretary to declare certain terrorism suspects stateless. The bill was initially blocked by the House of Lords in April 2014.[105] However, the Lords reconsidered their decision in May 2014, and the bill returned to the House of Commons before being set into UK law.
She, and her child-to-be, can be declared stateless, which means she could be refused entry to the UK (or any other country). I doubt whether the Home Secretary would have the guts to do so, especially for the unborn child's sake.
For the anecdote, I had a colleague in Switzerland who was stateless (apatride). He had a humanitarian kind of stateless passport, allowing him to travel (with difficulty, ofttimes) issued by the Swiss authorities. He was born in Krakow (Poland) of parents from an annexed part of Ukraine. Neither country would consider him as a citizen.