My cousin is lactose intolerant but not strongly so and can drink about 2 cups of milk before getting stomach cramps. So, she has milk on her cereal every morning but will skip it if she knows there is something else she will want later in the day. She used to sometimes say yes to ice cream if someone offered it and she was at her limit, but the cramps are quite severe.
Wheee, I'd skip the cereal every day, just in case a wild icecream appears.
(Maybe that's easy for me to say because I don't eat cereal.)
Though, if she really likes cereal, why not try soy milk or so? It's good!
Up to her, of course. But I think if I could only have limited amounts of an ingredient that commonly shows up in random treats, I'd try to take it out of my own regular food pattern just to be able to have those treats when they occur.