What happens if a woman does bench press??

It can build up your pectoral muscles which can make the breasts seem larger but they don't actually make them larger. Breasts are made out of fat so the only way to make them bigger is to gain fat or get implants.
They wont get hard like a rock either. I can bench 120 pounds and while I have small boobs (but I have always had small boobs. Lifting didn't cause that) they are definitely not rock hard. I still have boobs, I just built the muscles underneath.
You will only make them smaller if you lose fat. Benching itself doesn't make them smaller.

you'll grow a mustache

Why would you even ask this question?

Ok no, their breasts do not have muscles in them and there for no they would not get stronger like her abs or biceps.

I hope I helped, I guess.

Her arms will get stronger