Ivermectin is used for worms/mites/etc with dogs. Be careful with the dose, application, etc. as for dogs it will kill some breeds or make them very sick. Not sure if the same holds for chicks.
You could try to separate her out & give her a bath with environmentally friendly/dawn dishsoap. Use running water to help flush the mites off of her as best you can. I read somewhere about using a product called nustock I think it was. I've had mites on my sex-link that I've had luck treating with batch & coating (working down to her skin) with petroleum jelly then washing & repeating in a few days. The petroleum jelly can/will dry & flake off, but she might not like that. Just treat her all over as they'll move to an untreated area. If nothing else, might help give her some relief until you can get her to the vet after the weekend.
If you google at home treatments there are loads of suggestions.
Hope helps.