Hey Lyndz,
I would say that I believe that yogurt is processed differently than milk, which is why you can still eat cheese, yogurt and probably cottage cheese without any problems. For Grae, I would stop giving it to her for a few days (maybe three) and see if she's still spitting up. If she is, then try it again in a few weeks. It's possible that it's something she'll outgrow. Remember Muriel's baby, Elisa, couldn't eat anything, and now she's able to eat things she previously couldn't. I'd just continue to offer it to her every ten days or so and see how she does.
To answer your question I would think it's an intolerance, not an allergy. She would probably have a much graver reaction if she were allergic - rash, violent vomiting or diaherra (sp?). So perhaps it's something she can eventually tolerate.
Just my opinion, so I hope that helps.
You're welcome a bunch,
Lu