Weirdly enough this happened to me a couple of weeks ago for the first time ever. My client came in on my day off so I never actually saw the reaction unfortunately, but it was described as pus filled lumps around her eyes.
During her consultation and on her card she said she'd never had a reaction and wasn't allergic to anything, which turned out to be wrong as she hasn't realised the importance of telling us these things! She'd had a reaction the last time in another salon and said she'd been convince she was burnt, but felt differently now it'd happened again with someone else.
So anyway, I advised her to see her GP who gave her some antibiotics and then it all went down after a few days.
If you've done a full consultation and got her to sign a card or form then don't worry too much, there's not much more you can do. Just don't wax her again! My client has now tried threading and is absolutely fine with that. Might be an option.
Good luck, I know how scary it is when they have a reaction!! Xxx