I'll say that my treatment and yours are totally different to start with, but that said, if you received RT as a primary therapy, should should only expect a "dry" or perhaps "damp" orgasm. It is quite the different experience, and I've had it without the least hint of an erection (I'm not expected to have one, since the nerves are gone, but it doesn't stop me from trying).
And yes, the doctors told us all that things would get better quickly. We all think they lied. But yes, it takes time. And I think it is fair to say that working from no expectation is better. That way when something "wakes up" when least expected, it is good news, rather than a chain of failures when you try too hard.
You are going to be overwhelmed with responses from guys who have total ED here, and have to use one of what we call the "three P's" - Pumps, Pills, And Pricks (referring to the needle prick in your prick for an injection).
If it were me, I would give her a good hug, help her understand that it is no one's fault, and play the roles of a couple of teenagers trying to get away with something at the movie theatre, at least for tonight.