If "contact" bothered her I wouldn't use a flea collar -- they are VERY strong (and not very effective).
Sentry Natural Defense - it's essential oils but you spray it on sparingly.
Honestly I would NOT use **ANYTHING** until the skin is way beyond completely healed. You may need to use DE (diatamaceous earth) around outside or even in the house (you want the organic kind that is "food grade" -- better pet food places carry it usually) - you can even dust that on the skin *IF* need be.
I would assume that something else may be an underlying cause -- if it's been used that long then typically a reaction like that can be caused by the body being somehow ill-equipt to deal with it. But you want to make sure an infection like that is GONE GONE GONE before you stop antibiotics -- you don't want it returning only to have the dog then resistant to the antibiotics.
Have you used anything else that is systemic? Changed foods? Changed anything in your home? In other words, allergies can take MANY forms with a dog -- and if something has changed and it raised the dog's allergy levels then the first irritating thing could have caused something pretty huge. Does that make sense?
It's easy sometimes to just blame one thing -- but when you've used something for a long period of time and **suddenly** something changes you may need to look deeper, particularly if the reaction spread this badly.