Why does she always abruptly end a text conversation?

So I'll text her to say hey and she does the whole "hey (name) :) yadda yadda yadda" and we go for a decent amount of time. It's not like I respond immediately or anything. Well all of a sudden she won't text back and I don't keep texting her until she does I wait for her. Well if she's not saying anything I'll text her back

In a couple of days or so. But I mean I'll see her on Facebook and stuff but I avoid going on when she's on so I'm not awkwardly there. I'm not the one to get pissed over a text she never responded too but she does this a lot. We do stuff together in person sometimes. Why would she do this though? Why does she even respond in the first place if she's going to end the conversation like that?
Why does she always abruptly end a text conversation?
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