We brought a 1 year-old rescue kitty home and my 5 year-old girl kitty is mean to her. What can we do.?

Our new kitty is scared and our 5 year-old chases her constantly. We spray the 5 year-old with water to deter her, but our patience is wearing thin. Both cats have numerous boo-boos from fighting. I'm afraid one will lose an eye. It's been almost 2 months. Any ideas on how to handle them?