25 miles in a month isnt even really enough to keep the brakes from getting surface rust on them. Using it that little I doubt they even noticed it especially if it was just short trips up the road like our parts guys at work do. Unless someone stopped in front of them and forced them to slam on the brakes it probably felt normal, especially if it wasnt that noticeable when you bought it.
At this point I think your best reaction is going to depend on how they react when the time comes.
I could see them not doing anything at all if it wasnt there at the time of purchase. But since it was, any issue involving the operation of brakes could result in a serious accident possibly even someone getting dead out of it. Even just a warped rotor is going to effect the efficiency of the brakes. So you could argue that they sold you an unsafe car.
If they value their reputation they should fix the situation, however, since you didn't tell them at time of purchase they're going to stick by well you did something to cause it afterwards.
As I said earlier I don't know if brakes are considered a wear and tear item at 2 months after purchase on the warranty so they may hit you for the price of parts. But I cant see paying the price of parts and labor on something that was there to begin with. I learned long ago when test driving cars, especially used cars, any sound or vibration or anything that wouldnt be in the operation of the car brand new needs pointed out to the dealer. Especially in situations like this. But also to help get the car for cheaper. Alot of times if you point out issues like hey the brakes need changed, they either sell the car cheaper or repair it and still sell the car for the same price.