Jacquelyne, I had an aunt like that...she'd steal stuff from our house, the grocery store...anywhere. Once we found the remote control to the TV in her purse! Some ppl are kleptos and get a "high" from taking things...even things that are meaningless or that they can't use.

Anyway, my aunt used to make herself feel better by giving away the stuff she would steal. "Here, Mary, I bought you some perfume," and she hands me a half full bottle of Eternity with no cap and a TESTER sticker on the bottom of the bottle! She'd just lifted it from the make up counter at Kaufmann's!

She was also 198 years old when she did all of this, so age and maturity have nothing to do with it...it's like a sickness, I guess. Just keep your eye on your sister-in-law. You may just have to tell her that she is no longer welcome in your house because of her sticky fingers.