Try to make this short.
My older sister and i are 13 years apart. We were super super super close while i was growing up. Shes always drank way too much and couldnt even attempt to speak to her about help without her exploding. My oldest sons 20th birthday was yesterday… too old for a party yes but oh well 
even though my sister and i havent spoken ive reached out a few times since i got clean and she just says no. She cant let the past go. Thats her choice it sucks but i have to respect it. I have no clue why but she just decided to text me to try and get on to me… like im in trouble… im 39 years old… saying she hoped my son and little sister seen me for who i really am. I take several drug tests a month through my outpatient rehab. She didnt show up to the birthday party because it wouldve been “too awkward” i told every single person invited iff i didnt have something nice to say then i wouldnt say anything at all. This grudge my sister is holding shes seriously not budging. It hurts me. But i dont want to give up trying with her but at the same time i cant keephaving this same battle with her over and over.
Theres a lot more twist, things u never saw coming… could probably be a pretty good movie of im honest. Advice? Opinions? Anything helps
First off, that hurts. I think anyone would feel the same in your situation. I’m sorry 
What’s going on here is about her. For some reason she’s projecting pain or hurt out onto you, and it is coming out in the form of these out-of-the-blue hurtful texts. There’s a lot of reasons she may be feeling pain now specifically, and the only person who can shed some light on that is her. It may be directly or indirectly related to her history with you, which is why the texts to you are happening (I don’t think they’d be happening if there was no mental connection to you at all, even an indirect one).
What to do next is up to you. You can keep silent if you like. It is painful to receive those texts though (maybe there’s a way to temporarily silence her specifically on your phone?). You could also give a short, empathetic reply, saying that you can see how much pain and anger she feels. You can’t see it from her perspective - no one can - but you can see she is deeply angry and hurt. There’s a lot of different ways she could respond to that but she will definitely respond. Be prepared, be clear with yourself about when you need to take a break from the conversation and when you do take a break just tell her you are taking a break, so she doesn’t misinterpret your silence. (Emotional conversations are heavy.) Keep yourself polite and empathetic, and focus on validating her feelings.
Is she drunk texting you? I have a relative who does that. She is my most beloved and sweet aunt and she turns into a mean witch.