How to deal with jealous sister?

My sister can be pretty mean and aggressive. I didn't really get why until a few years ago, when she started talking about how our parents treat me better than her. There's little things like my father tending to pass me food during dinner without me asking (she often gets annoyed and comments when this happens). Now I didn't really notice it before, I don't think it's really a big deal, I'd rather prefer they didn't, if it would satisfy my sister.

Now when I am alone with my sister she tends to behave nice, and tried assuring me that she is only mad at my parents, not me. However, when I am with her + them, she is more often allied with them versus me. (making fun of me for not behaving socially normal etc.)

Now why I am worried. My sister can say some terrible things, like "just stay friends with our parents until we inherit their money", and once she told me I should behave more nice to our ill grandmother (I don't talk that much to her), but again, followed up with the inheritance being the reason. I just doubt I am really much different to her than these other people, when she behaves the worst to me when we are all together, despite being friendly when we are alone (this only started a few years ago, before that she was hardly ever nice). When my sister was younger, she was much more aggressive, and when she gets mad she will tell mean things people's face instead of behind their backs.

Although she behaves mostly constructively, she makes some disturbing comments occasionally, such as during a murder mystery TV show. She has commented she would definitely commit the murder too if she was in such a scenario, and that she can understand mass killers, as she may as well go and shoot some people if she wanted to kill herself. A real life case is regarding one of her ex-boyfriends, who she broke up with, and then she revealed some anonymous online identity he had, to revenge him. (She asked me "you understand I had to punish him, right?", however I don't know what issue she had with him. I am thinking maybe she tried making a warning to me.)

Now the problem? I moved away from my parents 5 years ago to take a master's degree, which I finished now. I moved back temporarily, as my house was for students only. I plan to mostly stay away from my sister rather than dealing with her, however something worrying happened last week. I was with my cousins (male, age 15 and 17) and we're pretty good friends. I lived in their cabin near the beach for a week, and the last day my sister + parents also visited. Now we were heading back from the beach. I was walking next to my cousins and my sister was walking behind us. She commented that I need to swing my arms in order to walk normally. So I started swinging my arms exaggeratedly, as a joke. Now my sister then commented to my cousins about how I behave strange generally, and claimed that I copy others people's affection showing behavior rather than behaving naturally (something like this, translated to English...) I found it a peculiar comment to make. (yeah, not a natural comment...). It seems like something she may have read of an Asperger Syndrome symptom description. (Note: I was diagnosed with Asperger Syndrome a few years ago). My sister said it like it was just a btw-style comment, but I am worried she has more malicious intents. She may be trying to hurt my reputation among my family, which is really the only damage I think she can do to me (legally). At least one of my cousins knows she's mean, and they don't pay much attention to her anyway. But my sister is good at manipulating people (for example, another girl accused her of bullying her in high school. My sister met to debate about the bullying with the principal, and "won" the case, and then the other girl changed school disgraced. I think they were both mean to each other, the difference here is: The other girl went into therapy due to the bullying, while my sister was amused by the whole thing). One way she manipulates is by constructing narratives about people, such as "you must want a Japanese girlfriend", which she tells me in front of my parents occasionally. This one hasn't become a big thing, but over the years, I fear many things we consider true about each others were just made up by her. And it seems most people don't really notice or care much. My plan has mostly been to get into work (programming), make some money and a name for myself, and forget about this whole inheritance $#%^. However, if I return and my family knows me more from what my sister tells them, it won't be very good...