This girl accepted my friend request on Facebook, and allowed me to follow on Instagram but NOT Twitter?

[john]

She is in one of my classes and I sit next to her, but I don't really talk to her since she is very shy. I found her Facebook, Twitter, and Instagram page. However, I found her Facebook page 4 months ago, and we have been Facebook friends since then. Sometimes she likes my post that I know for sure that she is into (political quotes as an example). Then today I found her Instagram and Twitter page, and I sent both request to follow her. She said yes to Instagram and also followed me, but not Twitter..?.?? Is it because her Twitter page is too personal, or she doesn't find it interesting to allow me to follow her? I also don't use Twitter that much, and I don't have a profile picture on my page. I also never tweeted once before. The only thing visible on page is followers, following, my profile name, and my real name. Any suggestions or thoughts?
She knew my whole name. It should appear on her notifications when I sent her a request. I don't think she had to see my profile picture to know if its me or not.