Family troubles.

I need some advice. So my sister and I got into a fight which she started about me not knowing about some office thing on the computer. I genuinely didn’t know and she went fucking nuts about it. She has quite a temper which I usually avoid. I told her genuinely didn’t know what others were talking about and she preceded to call me a liar, and an idiot. How would you have reacted? So I started to fight back. Obviously. I genuinely didn’t know. I was focused on something else and didn’t even hear what was said. She of course, like the little brat baby she is, stormed off to her room and all the while doing that she called me fat, which I am not, told me I had no friends, and that no one loves me. I had a breakdown because I tend to take this stuff personally sometimes. I should also mention that she’s older than me. I should also mention that when she’s not being a bitch she’s my best friend and I would do anything for her. She needs to see a therapist for this anger because she has gotten into many fights with other family members. Later that day while I was still crying i texted her an apology. Because that’s being the bigger better person. She never responded. She’s been avoiding me around the house staying in her room for 5 days. She finally comes down last night doesn’t say anything to me but this afternoon talks to my brother about how she “doesn’t know me” and whole bunch of other shit I won’t say. So anyways what should I do about this mess. Please leave me some advice.