My sister is acting weird for a couple weeks, and it just turned innapropriate and i don't know how to talk with her about this
Well, it's difficult to explain without seeing the entire picture, sorry if this gets a bit confusing since English is not my native language.
I (22m) am adopted since i was 7 years old, my biological father and adopted father were very good friends since childhood and policemen together, it seems i visited my adopted parents house often, but when i was 7 years old my biological parents died in a car accident, my father was a single child and my mother had only an older sister that lives in another country, Bio-grandparents from mother's side were already deceased, and Bio-grandparents from father's side were already a bit old, but they would take me in even if it would be difficult, but since my adoptive family was already close to my father's side of the family, they said they always wanted a second child but had no luck yet, just their daughter that was 6 at the time (21f now) and said i was almost part of the family already, so my grandparents agreed to make me legally adopted by my current parents.
All of this is the past, me and my sister were always close and friends, doing things together, movies and all, she was extroverted while i was more introverted but we got along very well.
However two years ago she got her first official boyfriend that i never liked, neither did my parents, the kind that was a party-goer and all, and we were all afraid and warning my sister this wasn't going to work but she didn't listen.
One year ago, he cheated on her and she became quite depressed, specially since he had a bit of an instagram audience in the area around our town since he ended up playing for the local team after graduating High school, and he badmouthed her after the breakup saying she was bla bla bla, and he cheated on her since the start and she would still go back to him after "some talk".
My father got very upset, i was scared what he would do, so i asked him to let me and my friends handle it, as it was a small town (50k people), i have some good friends, and we got to her ex and scared her, all big brother stuff, there was no violence of course, my sister got a bit happy despite she entering quite the sadness circle, staying home most of the time, sleeping a lot, but she got into therapy a few months ago and started getting into her feet more.
Now the weirdness, ever since that incident with her ex, i've been closer to my sister since she was depressed and needed support, my father is a police as i said and my mother works at a bank, so their schedule doesn't make them home much time to take care of my sister, i decided to lock one semester of my college to stay home to take care of her, and have just recently going back to college as she got a bit better.
But over these last months, she got even more clingy than before, often sleeping on my bed with me, touching a bit more just bordering on being innapropriate, but i never said anything to not upset her, but she has also been saying and asking some very strange things, like "We were childhood friends before being brothers", "It's good you are single because i don't want any girl stealing you from me", "Do you think we would end up marrying if you didn't get adopted by my parents" and other stuff, and i just say she is being silly and funny.
I don't indulge her in these questions despite they slowly getting more and more constant, along with unconfortable insinuations, in the past month has been a bit warmed than usual, so when my parents are working she is walking around the house wearing less and being weird all the time, but the straw was last night when i was showering and she just entered the bathroom and decided to shower with me there, she didn't touch me or anything but it was very awkward considering everyhing that has been happening, and she just giggled at me saying she shouldn't do that.
I'm struggling on how to say to her that this isn't okay more firmly, specially since she isn't exactly out of her mental health stuff just yet, i'm afraid she would just return to being reclusive if i got to stern or involve our parents (they are quite strict), aand she is due to take an exam to enter the same college as me in just a month, finally getting up her feet, and i don't want her to have more mental stress just before this exam.
What should i do? I'm thinking about contacting her therapist but i'm not sure if that would be a good idea, HELP
PS: Burner account for obvious reasons, too personal topic and my sister sometimes uses reddit for memes, again sorry if it got a bit confusing or bad english gramar
TLDR: Sister is acting weird and innapropriated recently after slowly getting better from depression, and i don't know know how to tell her to stop without breaking her trust and hurting her