how long will this last?

I have recently been in a fight with a family member of mine, my sister. My sister lives in L.A. and is four years older than I am. You would think she would have grown up and could be mature about things, but that definitely isn't the case. Over spring break, someone commented on a picture of her dog, calling it ugly. She became very pissed off by this comment and told me to "fuck off" because I didn't stick up for my sister, but instead my "boyfriend."

My sister and I have never gotten along that great. She's the middle child and feels like since I'm the baby my mom always takes me side. However, most of the time she's in the wrong so there's a good point of why my mom is taking my side. In this case, it's absolutely ridiculous why she's even mad at me for this. I told her over and over again I told him not to say anything and to apologize, but really it's just a dog.

My brother and sister's grandmother passed away earlier this week and they both came home from L.A, and Georgia for the funeral. This was the first time in years that we all have been home together. Did my sister say one word to me? Absolutely not. I even confronted her before we came home apologizing to her for everything and I hoped we could put it behind us in a time like this. I honestly don't understand how something this horrible could happen and you still can't talk to your only sister. Life is too short and things happen way too unexpected. Hopefully she'll learn this before it's too late.