is she trying to avoid talking to me on fb?

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there is this girl that is friendly with me, but she sometimes acts nervous around me sometimes. when I'm on fb, ill see that she would like some pages like 4 minutes ago, but when i click on the chat bar to see who is online to chat her name is not on it. i have to manually type in her name in the search bar and click on her name and then wait till the message that she is offline to go away and then when it goes away i can type to her. is this a mechanism to avoid talking to people on facebook? I've chatted with her before on fb and everything seemed to be going well, we talked about our favorite music and some funny stories i told her that she thought were funny.
she is my friend on fb