Aggressive Pup

Ladies, I need some help... so I have 2 puppies. One we've had for a year (Sable) and the other just a couple of months. Since I've been pregnant, Sable has been so aggressive towards our other pup. Anytime he comes near me or tries to play, she growls, barks and snaps at him. I always tell her it's ok he's just playing but that doesn't help.. Anyone had this experience? What can I do to get to stop? I know she's just protecting me but I feel bad for the new pup.