Why my bestie ignores my messages?

I used to text my best female friend every day every thing was normal, untel she went to college and she started replying late, I thought that's because she is studying (she is online but she reply within 4 hourse then she talk normal) but then she starts replying in more than 9 hourses or doesn't reply at all so I stopped texting her she"asked why don't you ask about me" then we texts each other for a while and next day I didn't sned anything she asked me again the same question, after while she came back to text me as we used to do but ignore me again for two days what does doing all of that mean and should I stop texting her?
Why my bestie ignores my messages?
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