Why is the girl i like doing this?

So i like this girl from work. i know she just broke up with this guy she dated for 10 months 2 months ago, and for the past few weeks we've been hanging out and getting really close, its pratically like we're dating. so i asked her yesterday if she wants to make it official and she said she would love to. but she didnt want people to know right now and we would tell people when the times right. i changed my relationship status on facebook and she has hers as in a domestic partnership with ehr bestfriend (her bestfriends a girl, i know its a joke and girls do that) but like. is she embarassed? or does she not want her ex to know? i dont know why shes doing it..