Tell her it's dangerous, anyway, then let the rescue center know about it. It is surprising that they let her adopt without having her agree to get the dog spayed. Tell her to seperate the female from the males right away.

That said, I am not sure, frankly that it IS dangerous to the dog, but she doesn't need to know that. What I do know is there are puppies and dogs being put to sleep by the thousands because of indiscriminate breeding.