Grandma over spoiling my sister?

Well, so recently I went on a Vacation with my Family and my Grandma was told to feed our Dogs and Cat. She decided to just spend the night there while we were gone and we really didn't mind when she called and told us that. Then our Vacation is over and we go home and she like invaded our house with her own stuff. I look in my room and see that she put TONS of stuff and decorations in my room. And the bathroom is just overstuffed with baskets of useless things (Example: Sock Purse, Bubble Bath, Soap, Plastic Flowers, and Sleep Masks.) I didn't complain or anything because I really appreciated it that she would do that. Then my sister tells me to come look at her bathroom. I walk in and see that it's even MORE over stuffed then mine. I normally wouldn't mind this but it was over stuffed with a lot of MY things. My brushes, Deodorant, Bobby pins etc. Even my stuffed Ugly Doll (name of the company) Was there sitting on top of her toilet. So I take all of the stuff back and my grandma seeing me carry a LOAD of things out of my sister's room probably gave her the Impression that I was jealous. By the way, all of that stuff that was in there I had in my room before I went on Vacation* I decided not to make a big deal about this because if I confront her she's sort of one of those people that says : I would really appreciate it if you did. or.. Oh I'm so sorry honey. I really didn't mean to. ( And basically begs you to do things and/or tricks) I'm not sure how to describe a person like that. So I go to sleep and the next day I go into the kitchen, she's asleep on the couch. I'm looking for my cat so I check in rooms and I go to my sister's room and check in there. **My sister is not there because she went to go somewhere with her boyfriend** My cat is in there and I see her go in the closet so I go in there to get her out because she usually rips up her stuff. In the closet is my Hollister Jacket, my Knee socks, my shoes, 3 Pairs of my Shorts, My sungles, my Fox hat and a bunch of other stuff I can't remember. I hear the dogs barking which they usually do when someone is coming down the drive way. I grab as much as my stuff as I can and put them in my room. To make sure who ever is coming down the driveway doesn't think I'm a thief. I would tell her or who ever the truth but if it was my sister she probably wouldn't believe me. If it was my grandma she'd probably say she believes me but I can't be too sure. So at this point I'm getting really suspicious about what else she has tried to give to my sister. So I go to my room and try not to worry about it as least as possible. I'm hungry now and go to the kitchen to see my Grandma showing my sister some clothes to try on to see if she can fit them. She holds up a pair of my pants (that were in MY closet) and my sister holds them up to her waist and says she'll try them on later. So I know my sister isn't going to speak up if she finds my stuff in her room. I tell her that they're mine and she replies with " Oh I'm sorry Hon. I can't really tell." When my sister is like a lot of sizes bigger than I am. I really don't want to confront her but it's turning out to be my only option. Another reason that I don't want to is: that one time we were in the car and I was messing with my sister and she was playfully saying "Stoopppppppppp." My grandma thought that I was really bothering her and said:" Stop I've had a long day and you need to leave her alone. I'm sure she doesn't enjoy that." My sister didn't object because she knows how our grandma is. After that my Aunt asked for my Sister to baby sit and I went along too because I thought she wanted me too. Then my sister was like she only asked for me. So clearly after that thing in the car my Grandma must of spread the word that I'm childish and immature. I wouldn't want her to do that again after she sees me taking clothes and items out of my sister's room. What do you think the best way is to do about this? I've talked to her about stuff like this and she still continued to do this. She also bought a lot and I mean A LOT of clothes for my sister, only telling me when I go to the store with her that I can buy anything under 30 bucks, when not too long ago my sister came home with 4 huge bags full of clothes from the mall. I really don't want to complain or anything but... I feel like she and some of my other family members like my sister more than me. She's made it so obvious. What is a good thing to do about this with out sounding Jealous or Complain-y?