Older rescue dog scared of puppy?

Your older dog may have never had experience or socialization with puppies / smaller dogs. This could potentially be scary for her, since their behaviors are quite different (hyper, active, playful, etc.) When I brought my second dog home as a puppy, my older dog hated him at first. She growled and got protective over her toys and food. However, this changed as time went on and they became closer. Now they play great and have no issues whatsoever! This is something that definitely takes time, since they still hardly know each other. Once they begin to understand one another's behaviors and mannerisms, things should become much easier. Definitely keep working with them on socialization and try to get them to engage in play with one another! I feel like your older dog will begin getting used to her as time goes on and hopefully they can become good friends!

Good luck!

It could be due to differences in energy levels, size, or even just trying to establish a pecking order. My parents have a 4 year old boxer that acted that way toward my boxer puppy until they got to the same height and my puppy had learned her boundaries. Now they love each other so it could take some time for that leadership to be established and the puppy to be trained a bit more. I would just supervise them closely until they have that worked out.