Sean Hayes' role (spoilers)

Well this was something I'd never seen before. I must admit, I made the assumption right off the bat that the character was a trans woman. I was looking at it totally from that point of view: I mentally congratulated Susan's Mother who seemed to completely accept her child for who they were, right down to using the correct pronouns etc. I also assumed the married divorced guy had a predilection for trans women and when her brother acted scornful or annoyed by her, it was only due to her lazy, self-centred ways, and not the fact she was trans. However, the old videotape scene had me reeling as they cast an actual young girl to play Susan in the old clips and that was when I realised that Sean was playing an actual cisgender woman. I try to remain PC and was wondering if this wasn't somehow problematic. I can't think of a reason to be offended but am curious if anyone else has taken issue with it. Discuss below :)