Yes, I have never made that choice, but when you raise the zombie-Connor, Mayrina decides to go to Baldur's Gate to find a way to truly bring him back.
Without raising Connor, I figure she has no incentive to travel to the city. So I think it is understandable she doesn't show up in Act 3.
I certainly didn't either give her the wand or snap it in front of her. Not sure if I spoke to her at all after finding it, but either way, she did turn up in act 3. If it's intentional (they might have just not thought about it), then it's probably because she's lost her farming life with Connor dying, and like everyone else she got drawn into the city. Doesn't explain how she got through the shadow lands so easily, but she did.