Dating

Why would my co-worker give me her facebook to only ignore/not accept my request?

We are very friendly with a cute co-worker. She and I go to different colleges and are both freshman interested in the business field. We have a lot in common so we talk a lot with her, we even flirt a lot and things get intense sometimes. The are lots of signs of attraction but I don't push any boundaries because she has a boyfriend.
So I asked for her facebook and she gave it to me and I added her. Three days later she didn't accept my request and when I asked why she said her facebook is personal.
Well I looked and she has 1,652 friends and I am sure she doesn't know half of them well.

Why does she do this to me?
Why would my co-worker give me her facebook to only ignore/not accept my request?
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