Mrs. Martin is to Mrs. Smith as Mr. Martin is to Mr. Smith. Just like her husband, this lady manages to be a blander, more generic version of her counterpart. She sides with Mrs. Smith in the great doorbell debate and agrees at first that Mary, the maid, has no right to tell a story. It makes total sense that she replaces Mrs. Smith at the end/re-beginning of the play, as they're almost indistinguishable.
On the whole, Mrs. Martin seems to have very few opinions of her own. The most amazing thing she has to share is that she once saw a guy bending over and tying his shoelace. Of course, to the company she's keeping this is a weird and wonderful tale. Everyone finds it delightful. For the moment, she is the life of the party. She also proves to be even more amazingly forgetful than Mrs. Smith, by forgetting her own husband. As we discuss in Mr. Martin's analysis, this absurd lapse in memory opens up all kinds of questions. The Bald Soprano's characters may not be deep thinkers, but the play certainly invites its audiences to be.