It was hardly "roll credits" at that point. Dr. Crusher made it very clear that this was too much, going too fast for her, and she was not going to get it on with the new female Trill host.  It was a very big deal to her.

With that said, it's no big deal about a female Dr. Who.  The Master regenerated into a female, and Missy has been an outstanding character. I look forward to the next chapter of Dr. Who.