am i paranoid to think my (27F) sister (36F) is trying to copy everything i do?

i don't want to appear like this is some childish disagreements or anything else of that sort, we've been having a on-going issue with my sister behavior for years to the point where lawyers and police were involved. 

she's been making our lives *** for a while and my parents health has deteriorated because of it, but she always has periods of time where she's "nice". it never last, she usually only fakes it until she can't bear it anymore.

she's been diagnosed with bipolarity but decided one day to stop taking meds, that doctors were wrong.

there is one issue among the dozens she has with us, and one of them is me. she quite literally said word for word she was jealous of me, i was born after and took the spotlight away from her, we are four sisters and i'm not treated better than the others but for some reason it's always me and not the others.

to get to the point, when she has her nice periods, she oftens buys alot of things to herself. 

one day last year, i mentioned i wanted to learn surf.

this summer she said she wanted to get surf lessons and plan to get a surf board.

i got a kayak with christmas money and saving last christmas. 2 weeks ago, she ordered a kayak for herself. she never even talked about kayaking before. 

3 years ago, bought a bike to get around town more easily. only a few months after, she bought a bike to herself, but not any bike, the EXAT same bike, exact same brand, a VTT, same price same everything, except the color. she only used it twice in those two years. 

i don't tell her any of my life, so one day she found out i had an internship starting in the incoming days. the DAY after i started my internship she told the whole family she had internships coming for her new training course. that was almost a year ago, she never had those internships.

i went star gazzing one day to spot shooting stars. she never cared about stars, it was something i talked about, she bought a telescope after that and bought books about stars. 

i can go ON and ON. i talked about buying a sea suit to go scubadiving, she bought a sea suit before i could, i'm not sure for what exactly because she doesn't do ANY sea sports.

i got into resin lamps and made one once. she bought a pre-made resin lamps and started talking about making one. 

am i freaking crazy? everytime i get something or say something she ends up buying it or saying she's gonna do it too. 

the kayak she JUST bought? she's AFRAID of the sea and drowning, when i took her on mine she literally almost had a panick attack. 

is this all in my head? it's getting more obvious than before to me, even my family comments on it, how it's weird, sometimes i'm not surprised by the thought that she'll one day stab me in my sleep like we see sometimes in the news. you should see the dark look in her eyes when she looks at me and starts screaming.