She is moving out!

So she comes home from work and doesnt go straight to the bedroom like she usually does.  I know something is up and something is about to happen.  So I finish cooking dinner for the kids and she sits at the table with me and says she needs to talk to me.  We go out into the garage and she tells me that she is going to move in with her girlfriend who is also divorced.  I am fine with that but how do we tell the kids?  I am sure that my son will be ok but my daughter will be devestated.  She wants to do it this weekend.  I have know idea what to do or how to go about telling my daughter.  I have alot of thinking to do.  Maybe I will through it out to my DS family.