LOL I like the idea of offering to SELL her whatever she picks out of your stash. I'd make it pricey too!!
Or as fast as she picks something up, take it out of her hands and say, "oh not that one, I have plans for it" over and over. Then when she stares at you, you can ask her why she thinks you would buy all that fabric if you didn't have plans for it. Heehee.