I don't think anything I could say will stop you from worrying. It is so hard because they cannot tell you how they feel.
I think you are doing all you can...and on Thursday you will have your answer. Perhaps it is nothing. They do limp occasionally for up to a year following surgery. As for her other leg, if the ACL was torn, I don't think she would be standing on it.
I hope that Thursday's appointment goes well. You might be pleasantly surprised. I had a foster who limped for a long time after surgery...and on her last appointment I was so sure that she had undone what the surgeon had repaired. She was fine!
It is so hard not to worry.