In the meantime, I'm not sure if it would do more harm than good, but if it were an absolute necessity for the time being, giving her a bath and cleaning her ears, I'd probably take her to the vet and warn them to use a muzzle on her. Ask that they help bathe her and explain that she's a rescue, so please don't hold her aggression against her. But she is in need of an ear cleaning and possibly a worming, etc. At least, if needs be, they should be able to gently sedate her, but in the least, would hopefully have more experienced vet techs at hand rather than at a groomer's you don't know, they might end up hurting her or suing you if the dog hurts them.
Also be sure she's gotten her rabies shot before she ends up biting a stranger.
At least by taking her to get the job done elsewhere, she might not associate you with those bad feelings. You may then slowly work on gaining her trust in brushing, cleaning her at home. Probably having her shaved down at the the vet's is a good thing too, then you needn't worry about brushing her too much. Buys you some time to bond and train some more.
(Edited - Instead of deleting my post, I just took out the "bumping up thread" part since I see MANY posts since. LOL (so ignore my unprofessional suggestion)