I'm really sorry to hear you have mites in the cage. That's a real nightmare having to do a full cage clean. I had something similar myself not long ago.
There are lots of different kinds of mites, and if these are visible in the cage, they're not the demodex mites that live on hamsters, as those can only really be seen under a microscope. So any kind of spot on treatment for the hamster wouldn't be appropriate. They have maybe come from some food. Do you freeze the hamster food before using it? That helps kill off any hidden bug eggs etc
Even though they don't sound like they are hamster mites, it could well be something that could cause a hamster to scratch a bit possibly. Glad the scab is healing up, but I wouldn't use sudocrem again. It may be too strong for a hamster, but also it's not particularly good for them if they lick it off and digest it.
Elusive usually has some good suggestions for what to use externally that's safe. You could also maybe give her a pinch of linseeds daily, separate from her usual food mix - they just lick them up - these can work wonders for skin and fur condition, if given daily, especially in an older hamster.
Did you ever manage to find a vet that was taking new customers? I know it can be hard in London.
