I'd send him a picture to his phone (if he has one) and ask him WHY should you have to wait until she gets a fever? Or send a picture email to his office and see if he will prescribe an antibiotic for her that you could start giving her -- if he agrees it's mastitis.
But the warm washcloth should help, and just take her temperature each day to make sure she doesn't get an infection. Feel the udder for lumps or heat -- as these can be sure signs of mastitis.
I have seen what I would call a "blown nipple" on a mare once. There was nothing really wrong, except the nipple had no shape, but baby still nursed just fine.
So, keep us posted on her!