That must be a totally contrived story. The terms "my daughter's friend", "my daughter's girl-friend", and even "my daughter's roommate" have mostly non-sexual meanings when applied to a woman during an introduction.
I had the same feeling when I read it - I wanted to link to the actual letter but can't find archived Letters on SFGate.com (it was in the Oct 25 issue). I boiled it down to the basics but Muriel seemed genuinely concerned. Like NW said, "spouse" would be easier than the tangle of options Muriel waded through. Hell, "friend" would work.
There really is no need to include the specific intimate details about someone's private life in such a situation. Would anybody ever think of introducing "my son, the masturbator" at lunch, to explain why he didn't bring a date?
My mother might, I get my overt honesty from her
