I don't suppose your friend realized what she was asking of you when she mentioned the apple core block. I am feeling the pressure you are under, so I have a radical suggestion that doesn't really qualify as the encouragement you requested:
Tell your friend you have realized that an apple core quilt would be dauntingly difficult and would take forever, and suggest a simpler pattern. Do you have some alternate stash fabrics you could use in place of the original ones that are already cut? You could then turn your apple cores into a long-term, no-pressure project not tied to anyone's expectations.