Could you help me identify this medical condition / possible food allergy?

A friend of mine has trouble processing milk-based products other than butter. She’s alright with a bit now and then – a bowl of ice cream, for instance – but too much, or too frequently, and she gets stomach pains.
It’s a fairly recent development, cropping up within the last couple of years. I thought at first that it was a lactose intolerance, but apparently most cheese has no lactose and gives her trouble all the same.