Girls, Why would a girl that has a crush on me hide the fact that she is newly single?

My colleague has a crush on me and is interested in dating me but we weren't able to due to her having a boyfriend. She split up with her boyfriend a month ago but has kept it secret from me (I found out through someone else) but still acts interested and flirts. Why would a girl that's interested hide the fact she's single?

Girls, Why would a girl that has a crush on me hide the fact that she is newly single?
Post Opinion