I'm sure everything will work out okay! I brought Tessa home when she was 10wks and my BorderCollieXLab is 11yrs. She wasn't too impressed with having a puppy in the house but after about 2 weeks, they were playing together like they had always been together. It was just what Misty needed to make her feel young again. She now runs around and plays with Tessa all the time now but if she feels like Tessa is bugging her, she will "correct" Tessa and Tessa then knows to leave her alone for awhile.
Give it some time and they will be fine.
