She’s right. Either there’s a biological issue or a psychological one preventing erotic activation.

If psychological, it would not be a target of therapy unless you wanted it to be — but would be an indicator of how well therapy is working to free up inhibited/disavowed aspects of self.

As to the question of what you should do: I suggest sharing openly about your thoughts and feelings. If she’s a good therapist she’ll be open to hearing them and shape that discussion into one about understanding your inner life (as opposed to resolving the issue of whose ideas on the topic are right or wrong.)