My sister is taking my friends away from me?

Okay this is a super long story so I'll try to make it short. My Sis came two weeks ago or so and She in 8th grade n 14 yr old I'm in 7th but just turned 13. Anyway today shcool today. after school I asked her if she made any friends then she said ya this girl named Miriam ( my cousin who is also living with me BFF) and Stephanie, who I really like and is my BFF sister. Anyway I don't think they are exactly much friends cause all they talks about was my Sis hair, ( but they can still become friends ) which got me a little just a little bit jealous cause Stephanie always liked my natural curly hair. Sorry if I'm sounding rude but my Sis ( she's actually my half Sis ) also tried to make one of my fav other two cousins like her better than me, now she became friends with people I didn't want her to. That's like another long story, but yeah she didn't do this because she couldn't make friends but because she wanted to be better than me and get better friend so she can brag! And it annoying. How to get her to stop? I will tell her when times right but what can I do without tell pls don't be offending or unhelpful.