Why does my 6 month old kitten have swollen lips?

I noticed my kitten started having swollen lips on her mouth, about 4 days ago. & I looked underneath but on one side underneath her lip looks like tiny little bubbles that can be popped. But she plays rough w/our other kitten who is 5 months old. I have been watching her eating patterns. & she hasn't ate less or ate more. Just the same. She still drinks water & all the things a cat that is normal would do. I haven't noticed changes w/her. But it just looks like her lips jut out from her mouth rather than being flat & looking like a normal cat's mouth. Or is it that she is just growing up & supposed to look like this? Was wondering if there is a vet or vet's assistant who could tell me the possiblities. Thanks.