She has got away with it because there is an ingrained pro-tory , pro-brexit bias in the Brexit Broadcasting Corporation going back many years. They are also very pro-FPTP and anti-PR.
I do know that some Tories accuse the BBC of a liberal/left bias and I think this relates to the social attitudes of the London based journalists which are progressive - pro equal marriage, strong on opposing racism and sexism etc. But this can co-exist with a right-wing bias on all other aspects of policy, especially brexit.
If in doubt, check out the CVs of their political commentators and producers.