SUBREDDIT: r/askwomenadvice
TITLE: Woman (24F) doesn't respond to my (25M) message, but wants me to send her another one…Huh?
POST: My friend asked me about her later and I told him I think she's not interested. So he talks to his SO, let's call her "Debra" who is best friends with Sarah and says to ask about what she thinks of me. I told him he didn't need to do that, but he wanted to, so I agreed. A week later Sarah and Debra are hanging out and Debra asks her what she thinks of me. And Sarah says that I should her a message, since it would be weird talking through friends.

I don't understand, I did sent her a message. I looked on Facebook and it says my message was delivered but not read. I just assumed maybe she say it pop up and read it without clicking on it or just ignored it entirely. 
I don't know if this is a mixed signal thing or maybe I am just not getting the full picture here? My other friend thinks I didn't show enough effort, and I have another who thinks I should let it go since she is obviously not interested. 

So I guess my question is why did she not respond to the last message if she wanted to talk and what should I say if I decide to message her again?
TL;DR: 
Meet girl, doesn't respond to Facebook message, tells mutual friend I should message her if I want to chat, why didn't she respond to message I gave first time?