Hi there. Well, in my case, five months went by between the time my boyfriend and I first talked about a MFM threesome and when it actually happened. We were talking about our fantasies and when he told me sharing me with another man was one of his, I was excited beyond belief - but it took me awhile to get used to the idea of something like that actually happening. It was my fantasy too, but never in a million years would I have thought it was one of my boyfriend's.
So it's good that you've talked about it, and you're right, she is just going to have to go at her own pace. If it is something that she really wants to do then she'll definetly do a lot of thinking about it, and let you know when she's ready to get serious. Good luck