Why hasn't my friend replied to my FB message?

[Angie]

I sent my a friend a message on FB asking if I could hang out with her during lunch and break. We usually never hang out together, hence why I asked. I know she's been on FB cause of her news feeds but she isn't replying back to my message! I told her that she could say no if she liked and I didn't want to be a burden to her friends (we don't have the same group of friends). I also sent her 2 videos that I laugh-cried watching. They were so funny, I thought she should see it. I think she read the message but I don't know why she isn't replying. Should I just casually ask if she watched the videos? That way, I'll know she read it and maybe she might answer me. She's not the type not to answer back.