Is there a non-awkward way to ask my boyfriend's mother what she would prefer to be called after this long?

As some of you saw over here, I have been invited to my boyfriend’s sister’s baby shower by his mother. Here’s the problem. I have no idea what to call his mother. In all the time my boy and I have been dating almost three years she’s never actually introduced herself to me and it wasn’t until recently that she and I became anything resembling friendly. She is very odd and somewhat drawn into herself, but can be very sweet when she opens up a little.

She has a different last name than my boyfriend so I can’t just call her Mrs. Boyfriend’s-Last-Name and I feel like the time past long ago that I could just come out and ask her if she would prefer if I call her Jodie or Mrs. Smith. Names have been changed to protect the innocent.

I have asked my boyfriend what she prefers and he has no idea. Furthermore, I have asked him to ask his mother what she prefers to be called and he always forgets.

Please help!