WEIRD/SHOCKED!

I had an ex boyfriend that I no longer keep in touch after we broke up because he hates me however I was close to his younger sister and his mom some what. His sister and I have always kept in touch even though his brother no longer talks to me and because they lived close to one of my relative there was once I visited them while I was visiting my relative.
A couple of months ago I was browsing through my friendster and facebook account profile and I saw some new pictures so being the kepoh (busy body) that I am I looked through the album to find out that my ex got married.
I was talking to his sister (because of the time difference etc I rarely talk to her anymore) yesterday and I congratulated her for having a sister in law and I even told her to congratulate her mom for me. Wrong choice of words I think! She started pouring out to me that she absolutely hates her SIL and she's never liked her even when her brother was just dating her. I was shocked to hear that but I didn't say anything because I didn't want her to think I was jealous or anything like that. Apparently the SIL have been using and taking her stuff eg. clothing, make up, magazines etc.. without asking her permission and honestly I know how this feels and it if it was me I would be absolutely pissed and angry about it too. I asked if her mom and dad knew about this and they all did. I feel sorry for her and her parents. Her parents because they are caught between a rock and a hard place. I mean what can the parents say? For her is because it sucks to be living in your own house and have to worry that your stuff is being used/stolen by other people and she has to lock her room now. I could not offer anything comment or advice to her because I didn't want to cause any more problems in the house. All I could do was to be there to listen to her and ask her to keep her stuff away properly but personally I just want to tell her that this has to stop and it sucks to have to worry about your stuff IN YOUR OWN HOME and TO LOCK YOUR ROOM DOOR FROM SOMEONE THAT'S STAYING WITH YOU!
My parents has always told my sister and I NOT to touch or use other people stuff whether is with or without permission that's why I don't like to borrow other people's things. When we are living with other people we should follow other people's rules. Apparently her SIL not only uses her stuff but is lazy. Their mom runs a little food stall and works really hard all day. She has to come home and clean the house plus their house (because their house is adjoining with her house). She also has to go home and cook dinner for every one and the SIL DOES NOT do any of the housework to help with ANYTHING! I feel kind off bed for the mom.
Although it's none of my business but I could not help feeling really bad for this girl. She is not my sister or my close friend; she's an ex's sister but she's still a friend. We have kept in touch these years and she's like a little sister to me. I wish I can give her fruitful advice but I'm afraid I'm not in a position to give her any advice because I don't want to cause any conflict in their family. All I can do is to listen to her and support her in anyway I can. I hope that she can eventually get along with her SIL or else it'll be bad for her, her family and her SIL. Good luck my dear girl and I want you to know I'll be here to listen to you no matter what.