Is it recommendable for my sister to tell my cousin information even though my cousin copies and bases her life on my sister?  
Note; this is not just idolizing, it's a silent obsession for my cousin. This has been happening since we were kids.  
Examples that my sister made:  
1. I told her what my dog's name should've been, she didn't even hear of the name nor its story, when she got her own cats, she named one of them the name I told her, and when I confronted her about it she didn't answer my question and changed the topic.

2. When we were talking about our plans for our weddings I told her what I wanted my wedding theme to be like then she decided to want that theme also even though she gave a different answer at first.

3. One time she broke my little brother's Xbox and she showed zero remorse for my 8-year-old brother's crying, but when I scolded her and got angry that was the only time she ever showed any guilt and cried excessively .

4. Whenever I'm around her she has a whole different personality but when she's with other people, she copies my personality and basic mannerisms, she sees the way I act and turns into her own.  
(biggest red flag)

5. When I got back into one of my hobbies she decided to get that as one of her hobbies also (but failed after a couple of days)

6.  She only ever acted as if she cared for my little brother, but she does every small thing to sabotage his life because she sees him as a threat.

7. One time, I told her I love Attack On Titan, and then she started fangirling over Levi Ackerman even though she does not even watch Attack On Titan.

8. I told her what type of guy I like and the second I told her that she decided to like it as well even though she had a whole different answer than mine at first.   


And there are a lot more stories that are too personal, but you get the gist of all of this.   
Brother Again: She also told my sister a lot of times that she wanted my sister's life or lifestyle. At first, it seems like admiration but over the years, it got more obsessive and passive-aggressive. I want to know judging by all of this, is it safe for my sister to be around her?