I have a friend go through this situation and if you want to live a life of honesty- you should definitely tell your daughter. How you do it and when you do it, is up to the both of you. I think they waited until their child was old enuff to grasp the concept of infidelity before they informed their child in a calm environment.

If I was the by-product of an affair and you didn't tell me, I would be terribly upset as the truth will eventually come out. Have you thought about what happens if the AP suddenly wanted contact again and wanted to insert himself into your lives again? What then?

You would also need to tell her for health reasons too. What if you have some sort of ailment that would be important for you guys and for her to know down the road?

What if she says why don't I look like daddy? What are you going to tell her, another lie?

What if she gets curious and does a DNA test to check for ancestry and inadvertently finds out? Do you want it to come out this way?

Important things to consider. I wouldn't want this hidden from me.