Dog with limp

I'm taking my dog, a 15 pound shih tzu mix to the vet on Monday, but in the meantime I was hoping to get some advice/information in case anyone has gone through this before.

My dog slipped while I was giving her a bath, she did not cry out in pain, she played after her bath, had her walk and everything was normal. I only noticed the limping at night after she slept for a while. I thought perhaps it was just a one time thing, but no, she limps after getting up but the limp only last a few seconds and then she seems to walk fine.

I gave her a few days to rest, reduced her walking time and haven't allowed her to jump/climb stairs. It's been difficult, she's a very active dog and she wants to play and run. Her appetite is fine, she's pretty much normal in every way except for that bit of limping she does after getting up when she lies down for a while to rest or sleep. She hasn't gotten any worse, but I also don't see any improvement, which is why I made the vet appointment.

I suppose my biggest worry is that this is an acl tear. Would she be able to walk fine after limping just for a few seconds if it was an acl tear? I've tried checking for swelling/heat and pain, but nothing.

I've taking a video of the limp to show the vet since I'm sure she won't be limping when I take her in, she doesn't limp when she's walking for a little bit. I hope it's not bad news, she's young only 3 years old, and she's such a happy dog. We'll see, but any advice is welcomed and appreciated.