Actually, I know a woman who ended up as an astronaut with NASA. A pilot, and a PhD in, I think, marine biology. Is it likely? Not really. Is it possible? Absolutely!

OP would need to look hard at the options for her as a UK citizen. Remaining a resident there, there may be no pathway to the space agencies of the US, the EU or Russia. Private companies should hire too (and I bet they pay better!). Either way, I’d pursue a lucrative and rewarding career before getting myself hired for an astronaut role!