Well girl....somewhere along the line you must be doing something wrong......
First, the diet change will take some time to show effect, all the bad stuff has to come out of her system.
That said, I noticed bugs develop resistance to a repellent. So switching every once in a while will help. With Repel X I noticed that especially. I used Mosquito Halt, works like a charm, lasts actually 20 hours. Now im out, I need to mail order, so I got ultra shield. Doesn't lastbas long, but works too.
What im doing is applying it other a mitt. Seems to "stick" better that way. Paying special attention where my Snipper seems to bothered most, chest, neck, face and girth area.
I also found a bug killer just yesterday which is hanging in their three sided shed. It was full of bugs during the day yesterday before hanging the thing, this morning....NOTHING, not one bug. I can tell they spent a great deal of time in there by how the bedding was searched for oats kernels(I feed oat hay and what is wasted goes in there as bedding).
The stuff is called Prozap Insect Guard. Im truely amazed, I have to say.
Apart from that, I don't wash her, don't apply any ointments, just wipe my fly stuff on early evening. All her fur has grown back, no more sores.
With her I don't think it's sweet itch, tho.
I did have two mares with it and what helped them was usingg Skin-so-Soft Original bath oil, wiped on early early in the morning and about an hour before dawn. They both stayed outside, stopped swishing and shaking immediately.
It has to be applied twice daily and has to be the above named, not the other scents or variations.