After being dairy free for a month, if you just give her a full glass of milk she should show signs within an hour or two. She would get diarrhea, pain in her belly, painful gas, nausea, and possibly other discomfort. If you're giving her yogurt you likely won't see much since yogurt has live active cultures in it and it sort of "digests itself" so that someone with lactose intolerance (that does not have a protein allergy) can eat it.
You should also be checking the packages of cheeses you're giving her. Some brands, like Cabot and Kraft, add lactase enzyme (the enzyme in the small intestine that digests lactose sugars) so as to make the cheeses lactose-free and the nutrition information on the back reads as "0 grams lactose." Usually it's the cheddars and the shredded mozzarella. You also might not get much reaction from real Swiss cheese or Parmesan cheese because of how they're fermented. Or from Kraft Parmesan which definitely has the enzyme in it.
Point of story: make sure that what you're giving her isn't actually lactose-free or chock full of live active cultures. Just give her a big tall glass of real cow's milk and you'll do fine with the test. Or you tell the doctor that you aren't sure if it worked and request the Breath Test where they test the amount of nitrogen in her breath after a small fasting period the night before. That morning they'd give her a lactose solution and have her breath out into a tube that catches her breath, then measure the nitrogen in it... if there is any nitrogen, she's lactose intolerant.
I have a child with lactose intolerance. We've been through this whole thing. It suuuuuucks. But it's worth it to figure things out.