Don't worry it can happen sometimes, but there is a tint remover available for that job if it happens again.
Applied with cotton bud if it is so close to the eye or let her do it with the remover on.
Don't wax it off it just needs a little firm rubbing and then wait until nature lifts the colour out with sebum or sweat from the skins pores, which will take a couple of hours .. Apply loads of moisturiser or use a good facial oil on damp coton wool is what I do if brows get overspill on the skin.
I know it's too late , but you can blame her for having such dehydrated skin in the first place, because it really is a reason that the tint gets carried into the upper layers when it is so very dry. So advise she moisturises before she comes and gets prepared in case it happens again.
Have you contacted her or seen her since yesterday?