Dog advice? Sorry if not allowed but I’m desperate !

I really need some advice with this - this is my German Shepherd, Skye. She has arthritis in her legs and about half a year ago she would have these episodes after she gets excited where her legs go stiff, she would lift her one leg up and cry a little bit, then she’ll be fine like nothing happened. Recently they’ve gotten so much worse, she’ll have about 3-4 episodes on a short walk and they’re just getting worse. Sometimes her back legs go stiff and she lifts them both at the same time, almost like a handstand! After that, she was on the floor, literally screaming and lifting her legs. This only happens when she gets excited, hence why I believe it’s something linked with idiopathic seizures.

We’ve taken her to the vet numerous times and he always says “oh it’s just her arthritis” charges us over £100 for medication then that’s it. We thought she was going to die with this video, sent it to him and after 4 days still no response. We asked if we PAID him to watch the videos could we please get an opinion, he instantly replied and said he’s he’ll do so if we pay him, and we did because we’re desperate to help her. Again, he said it’s arthritis. I’ve never seen anything like this in a dog so I’d really appreciate some help, please.

If this isn’t allowed I apologise, I’m just really desperate to get some input. I plan on finding a different vet to get a second opinion.

Thank you if you read this!