We have a problem with our older dog biting and hurting the 1 year old pup both females and spade?

Our Labrador/Staffie female(13 years old) will not accept the baby we recently got, sheepdog/Alsatian female,( 1 year old) they have both been spade - it is now the second time that she has had a serious fight with her - she locks on and wont let go (goes for her throat) obviously the pup is playful but not aggressive at all. Fortunately she has thick hair so the physical damage was not serious but very disturbing.