Would a transgender female be fertile?

It depends. The term "transgender female" is ambiguous. If you mean a transgendered person keeping their original parts, then they will be fertile as long as they are not taking hormones and have no medical or physical problems.

If you mean an actual transsexual woman, then she will never be able to reproduce as a female, and after her genital correction surgery, she won't be able to father a child either. If she was born intersexed, that is a different matter, and she might be able to reproduce as a female if those parts are functional and intact.