Sounds and looks like she's growing up, MDS.
Angela's advice is spot on. Your dau needs to understand those things, otherwise she could get real confused about who she is.
But you are also very right in not turning your dau against your ex, or running your ex down in front of your dau. That might make her feel like she has to "choose" between the two of you, and that can get very messy.
I take it your current wife has a good relationship with your dau as well? Do they talk much, girl-like? Maybe some outings together might let the conversations freely flow.
Cheers
Mick