LMBO I can understand being excited over her wanting to learn, yet being protective over your turf too :D:D:D
Maybe make some rules over what you are willing to share and what is off limits?
Most teenagers are very opininated regarding what would be awesome fabric and what is ugly to them... Maybe she needs to start her own scrap stash? Some 1/4 or 1/8 yd cuts?
A machine of her own from a thrift store to start out on?

Tell yourself that she may soon want her own machine in her bedroom and then she will be partially out of your hair. She still may raid your stash though.......

My DD is just wanting to learn to sew and she's 26, it took her having two girls and wanting to make them things befroe she decided to get creative! The lessons start this Tues., wish me luck! Enjoy your time with your DD, they grow up so fast and have their own lives. Mine now lives 1100 miiles away from me and I treasure each and every moment with her.