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?