I'm 16 and my step sis is 17.

Normally, she's warm towards me and engages in friendly conversation, but recently she became cold and avoids interaction with me unless it's absolutely necessary.

She's engaging with everyone else in the house except me, and when she realizes I'm near, she becomes quiet.

This isn't the first time this has happened. At one point she didn't talk to me for a few months. She would tell my biological sister how much she hated me for just about anything, regardless of how irrelevant it is.

Even with all that bitching, I just didn't mind it and enjoyed my life as usual, and it pissed her off even more.

When I came back from a road trip with cousins, I got everyone at home a present (yes even her). I left her gift by her door, and she ends up breaking down and apologizing for being a cunt, saying that life was being such a bitch to her, so she'd take it out on me.

Everything was pretty good until recently. I'm noticing these patterns again though.

My approach is just letting her hamster sort itself out and just do my own thing.