Oh, lord. The barfing is one thing, but HIDING IT? I'd want to punt her, too!
Maybe a Tide pen, or some other type of bleach pen, would work?
At least the quilt is still unassembled so you *could* rip out the stained blocks pretty easily if it came to that. Depending on the construction, you might be able to perform surgery and replace the stained blocks without ripping out every piece.