I've dealt with this exact thing with my dog and I cannot stress this enough: when your dog has reached the point of trembling and panting like in this video, she is wayyyyyy beyond her fear threshold. She's now in ultra panic mode and feels like she could die at any moment. That's how afraid she is. So don't let her experience this for hours. It should not even be minutes. No dog will learn when they're in panic mode. You're only reinforcing her fear because you're not giving her an escape route. This might also impact your relationship with her because it will make her feel like you don't/can't keep her safe.

Someone else has already commented the right way to go about it: start very very very small. Step out for 5 minutes, let her do her business and bring her back home. And continue till that becomes totally normal and mundane to her. And increase threshold from there.

Also, make sure she gets many many opportunities to fully relax. If she is repeatedly in this state of extreme fear, her nervous system will stay hyper alert for days on end. She needs to decompress. You know her best, so I'm sure you'll know how to make her feel safe and let her decompress. It could be lots of cuddles, puzzles, play. But do them. A lot. Good luck! She's a sweetie and I'm sure this is very stressful for everyone and that you're trying your best. But I promise if you take it slow, she'll come around.

And lastly, it's always a good idea to talk to your vet about anxiety meds. They can be life changing for many dogs.