What do you think of my friend...?

So basically I said hi to her on Facebook chat and she said hi and then immediately said brb (be right back). She was gone for about 20 minutes but on chat it didn't say she was idle which it should do if she hasn't done anything on Facebook for over 10 minutes. Then she went offline without saying anything to me. Sometimes she acts like a great friend but I can't help thinking she doesn't really want to be my friend. Like it's always me who texts her first and says hi first and sometimes she doesn't even reply. What shall I do?