A few years ago, well more than a few at this point, but it seems like yesterday, my Kelly went out to pee. I saw her squat, then yelp, and hop a bit. She did her business and came back in the house. This was in a area with lots of mulch and I did not see anything over there but it looked like something bit her.... But I did not see anything and I just happened to be watching her for some reason.
A few hours later I was working in the study and she of course was there watching me as usual. She looked at me kinda funny and then tried to get up and just fell over.

Eventually she did stumble to her feet but her back legs had gone weak on her.

She was not in obvious distress so we just kept an eye on her.
In the morning she was fine.
Eventually she had this mass infection at the base of her tail. It was the size of a hand ball. It took quite a few courses of antibiotics over a long period of time to get the infection.
I have not idea if the infection was a part of the lameness but it was curious.
Years later Kelly developed lameness that started in her back legs and it affected her back, neck and front legs. There is a genetic problem with GSD and Wiemeraniers that can cause this problem. Lots of tests and no real proof of what was her problem. For a good part of a year she had lost her ability to feel if she had to poop. I would get up a couple of times a night to let her outside. Sometimes she went outside. Sometimes inside. Our finished concrete floors made clean up easy. Or easier than carpet.

But after a while she could not even make it outside anymore. Cleaning up poo was easy.
But then she lost bladder control and that was the end. She would leave a 30-40 foot trail through the house which took forever to clean up. And it shamed her. She could barely walk at this point so the vet came to the house to end our suffering. It was time.
I wish we had known/thought about Lyme. It is all over our area. I THINK the wife and the vets talked about this but I just don't remember now. Kelly certainly had enough blood work done. And she had been pumped up with antibiotics so Lyme was likely not her problem. It was more likely the gentic issue.
Hopefully your dog will just recover like Kelly did. Dogs are tough and resilient. Your daughter does not need to loose another pet. My kids have handled the passing of Kelly and Chase very well. They really surprised me how they handled it. Much better than I when I lost my dogs as a kid.
We have a Golden for the wife and kids. She is a good dog. But after Kelly there are no more dogs for me.
Good Luck,
Dan