Erin, I don't really know much about this transaction and so its not pointed at you at all.
Often when I read questions similar to this I wonder why the framer even took the job in. I mean just the question is proof that you don't know how to clean, remove, or repair the piece. I keep an eraser at the design counter so when a customer asks, "can you remove the smudge" I hand em an eraser right then.
I have never received a piece stuck to glass but I can tell you that when I do, I will either suggest that we scan and reprint it or politely tell them to return when they remove the photo from the glass (I don't know a photo conservator). The reason I think this is so important is because you look more professional knowing your capabilities, even if that means you just refuse the work.
Carry on.