you know, it might actually be someone else. Your opinion seems to be greatly influenced on what other people say about her and not her actions. I steal peoples lighters all the time just totally on accident and I can see the sunglasses thing if she has a bunch of pairs that look similar, she may have seen them on the counter and thought..."I didn't know I brought my glasses in...fuck me." then stuck them in her purse.
I also had a friend accused of "stealing" a necklace from someones house and it ended up being found under the accusers car seat. My friend was pissed off that girly had such a low opinion of her.
Ask your brother if he has seen your runes and stuff around his house, go around her to check up on it and if she doesn't have it then stop being pissed off at her. If she doesn't have your stuff, then she didn't do it, and stop listening to brother B he may be just stirring up drama, guys like to see chicks fight.