I agree the rescue center should be informed.It is against every rescue I know of to breed.They should all be neutered and spayed.I think she is to young to breed her healthily but I am not an expert.It is true however she will keep them away until she is ready and then they will mate.If they are not seperate she will get pregnant.It is completely wrong.Please encourage your friend to do the right thing.She rescued these babies now don't make more babies that need rescueing.Not to mention the effect it may have on momma who is just a pup herself.