Loki is finally home, but older dog is not happy

Our new puppy Loki finally came home yesterday at 8 weeks old, its been a great start only had 2 accidents so far fingers crossed it lasts. He does have the runs tho, it was normal the first time. He's on the same food as he was at the breeders as she included a large bag of it. The other pups have been fine so far as we spoke to the breeder this morning. Our other major concern is that we rescued a 6yr old female lab about 3 weeks ago, we were told she was good with other dogs which she is, loves playing with my mother's dogs, but she will not tolerate the puppy at all, constantly growling at him, barking and snapping the air when he moves anywhere near her, she's withdrawing from us too prefers to hide up stairs on her own, refuses to enter a room he is in, reason I'm worried is that the rescue told us she was rehomed due to the previous owners getting a new puppy and they didn't get along. I'd really hate for history to repeat itself again as she's such a lovely dog. Is this behaviour on her part normal and will it get better or will we need to seek professional help to help correct this behaviour before something bad happens