Oh my god, please don't tell me they re-use the wax! That is the most disgusting thing I could imagine.
I would assume they do not re-use the wax and that the beautician wears gloves. If this is not the case, I would ask her "aren't you going to wear gloves?" as if for your own protection. If they re-use the wax, I would run. Think about it. That's disgusting.
The one and only time I was waxed (facial hair) the lady dipped a spatula into a small vat of wax, applied it, and I think (not totally sure) she redipped it to get more. I later had a bad allergic reaction to the wax (or the waxing process). I wondered if the problem was from contaminated wax. I think it is a possibility.
The ONLY way I'd ever get waxing again is if the salon uses individual sized waxing pots and throws them away after individual use.
So, all of that to say I think you'd be on the safe side to tell her know.