And breathe
I know these things can get stressful but your hammy will probably settle down again. They don't cope with change well at all so a cage clean and a new substrate will be adding to stress probably as CMB says. And yes maybe she needs to burn off some of that stress by being out a bit more at the moment. Until she settles down again, try and avoid any cleaning or moving or changing anything in the cage - for at least a couple of weeks. I should think the vet visit stressed her as well.
As for the bar on the Barney - that is a total pain! How long have you had the cage? Zooplus are quite good over issues and damage, if you haven't had it long. Send them a photo of the broken bar and they might sort something out for you.
Our last hamster went through something like this after we'd been on holiday and taken his cage to someone else's house, then back to our house. It was quite stressful and he also started bar chewing and wanting to come out all the time. I did give him extra out of cage time and ended up setting up the playpen round the cage (which was on the floor) and leaving the cage door open all evening so he could go in and out (but still needed observing in case of escapes so it took up a bit of time), but as soon as we closed the cage door again he started going crazy and bar chewing again. But if we put the lights out and left the room he stopped - so it was an attention thing.
In the end as soon as he started, we put the lights out and went to bed early. I would pop down about midnight in the dark and he wasn't bar chewing. But it took about two weeks of extra out of cage time, and early lights out before he settled down and stopped. Maybe she doesn't like hemp! I think that's unlikely though.
You can't get mites from plain toilet paper. I don't know about the itching but they do groom and scratch quite a lot, and that's quite normal. It's only if you see sores and it's really excessive scratching you suspect mites.
She probably doesn't know what's hit her after the vet visit and then her whole cage smelling totally strange as if it's someone else's cage. And on top of that she's female! They come on heat every four days.
Is her cage in your room? And the bar biting driving you crazy? Maybe try ignoring her a bit, and giving the out of cage time at a regular time each night so she gets into a pattern of when to expect to be out and when to expect to be ignored.