Overthinking need advice and help

Okay basically this is gonna be very long but about two years ago this girl had a misunderstanding with my sister and said her sister would beat her up and what not but I was the only one who saw because at the time my sister didn’t have her phone thankfully anyways the girls sister and I are friends and nothing has ever happened.The girl who had “beef” with my sister never even speaks to us and we haven’t seen her and when we do she never says anything to us (she doesn’t go to our school or anything).However recently I accidentally added girls sisters friend (yh ik that’s rly long lol) and I wish I’d just unadded her but since she knew me I didn’t want to start a problem by un adding her anyways she accidentally called me and for some reason that scared me so bad anyways like a week after I unadded and nothing even happened but Im constantly overhung this and after like months I had finally gotten over it but then a few weeks ago my youngest sister said that someone asked are you ,my name,’s sister and that made my overthinking come back but idk why and my sister doesn’t know who it was.Anyways I feel so stressed about this even though I bet the girl and everyone has forgot and it’s just me who is over thinking this.Idk why I should do give me advice I was thinking of telling my best friend about it to maybe help get it off my chest and forget it but I’m really mad that I’m wasting time worrying about this when the girl is probs living her life.I hate her so much I hope she goes through something miserable and karma gets her.Sorry for the rant but that’s just been very overwhelming and ruined my life.

Extra context:The girl’s mom and my granma are kinda friends and me and the girl are of the same background I have a feeling that’s why she didn’t do anything