Deal breaker, but honestly you need to make sure it's out in the open from the start. Relationships are full of compromises big and small. If it's something neither of you will compromise on well they need to ask themselves will they be happy in 'X' amount of years. Just because it's her body and she doesn't want to have kids doesn't mean your future happiness has to take a nose dive and i'm not saying force her to have kid's i'm saying that some people need children in their relationships to feel complete, reproducing is a natural bi-product of biological creatures. There are plenty fish in the sea, find someone more compatible with you (male or female).