Growling and biting puppy

by Rochelle
(Perth, WA. Australia)

I have a Jack Russell Cross Maltese, shes always been so friendly and gentle with other dogs, she especially liked my old neighbours dog who was kelpie. So when i moved in with my partner he decided to get a kelpie x american staff. They got along so well at first, always playing and cuddling together. But now i think shes starting to get sick of the new puppy, we've had him about 10 weeks now and shes bitten him on the nose a few days ago and he was bleeding. She also growls with a ball in her mouth and tries barking/biting and chasing him when were playing fetch at the park. Theyre walked twice a day and sleep inside and given so much love and attention i jusst cant think of what else it could be. Please help me! i just dont want her to hurt him or be growling and agressive towards him :(