I'm sorry this has happened to you.
Honestly idk how to make an e collar or how to put one on. So I understand what that's like. I do think the e collar is the best thing for her right now. Google how to make an e collar and try to make one and put it on her. Two things can come out of trying. 1 you succeed and she is now unable to mess with the wound or 2 you fail and there is no harm done.
If I were you, I would try to find another vet. If they aren't going to see her asap find one that will.
Best of luck. I hope you can find a vet and she gets better.