I have been selling some of my unwanted baby stuff as it's cluttering the house and tonight DP has had a phone call from his sister demanding everything she has bought my DS back as "she's not paying good money for it to be sold", none of the things she has given us has been put up for sale, she didn't even ask if it was the same items and after DP told her this she still went on a rant (I could hear her on the phone from the other side of the room).
At the end of the call she had the cheek to ask when she could take my DS. 
I am fuming, I have had to put up with her erratic moods for years and have just ignored it, even when she was in my house about 3 days after DS was born and went into a mood because other people were holding him (her parents).
I am fed up with it and have boxed everything up that she has given us and phoned her parents house (she lives there) to say it can be picked up whenever she wants.
I don't want to feel that I owe anyone anything, I also don't want her to see DS anymore.
To make things worse I am meant to be her bridesmaid in a matter of weeks but I will be giving her the dress with the things she gave DS.
AIBU and acting over the top because I'm upset?