If a sketch was pictured in anyway in the 
auction, then the buyer was allowed to assume 
there was a sketch and the description should 
have stated there was no sketch.  

If there was no picture at all of a sketch, then 
the buyer was wrong to just assume a sketch was 
included if you didn't say anything about it.

And personally, I would just ignore her.  You 
have your money, they have their cel, the 
transaction is over.