Yeah, she had done all the basis (washed hands, no hand cream, cleaning of the strings with a cloth after use), but her hand can't help but sweat! Meerket, I really do sympathy with you and my student
Something funny though, the letters had also wear off from MY computer keyboard, but that is after 2 years. I can type without looking at the keyboard (sort of memorize them like i memorize the piano keys

), but when my friends come over, they complain about me not changing the keyboard. Finally they give me a new keyboard as my birthday present 1 years ago

Never thought it has something to do with acidic hands though! But my fingers do not sweat normally, unless I am nervous. But so far I had no problem using cheap strings or Daddario and Dominant strings.
Maybe Dominant string can try solve her problem? I have to check whether it is possible to buy just an E string separately for now

So hard to buy separate strings over here. Most are sold in whole sets.