There's not much you can do about people who 
don't read listing and/or don't ask questions.  
My advise is to tell her that she SHOULD have 
asked the condition of the cel.  In fact, I think 
that  ebay states something to the effect that 
bidders do just that BEFORE they bid to make 
certain they know what they're getting.  

I had someone once complain that I didn't mention 
in the listing that the cel and sketch were stuck 
to a Last Unicorn cel I had up for sale.  This 
was inspite of the fact that in the listing it 
clearly stated that: 1) I don't open the cel bags 
anymore when I get cels because the lines fade 
quicker (in my experience in collecting for over 
5 years) and 2) Last Unicorn cels are so old that 
they typically come stuck to the sketchs (if they 
come with sketches at all).