A good first question might be, “Hold old is your daughter?” I take it this your daughter from your previous attempt at marriage.
If she is under 4 or 5, she shouldn’t understand anything.
If she is between 5 and 9 or 10, she might have a vague idea, but it would have to be more the contribution of what she’s being told than what she understands. She then needs to know her daddy loves her, her daddy ALWAYS loves her, and he is ALWAYS going to be her daddy. You can try to explain it, but it’s a hard concept for grown-ups. Reassurance, along with ice cream and hugs, is needed in large doses.
A tween or a teen might have a better understanding, but the younger she is, the more she needs to know that this does not effect her; that it is ecclesiatic or “church-related” in nature, and little old Canon law 1137- along with reassurance that her daddy loves her, her daddy ALWAYS loves her, and he is ALWAYS going to be her daddy.
An older teen or young adult might give you a rough way to go, particularly if she wasn’t too keen on the divorce in the first place. Unreasonability in this instance can be met only if the daughter is willing to listen. You’ll have to catch her when she’s calm, when she’s away from the other parent, and when she is willing to listen to what you have to say. You can use a book (and the …Wedding That Was is very good). You can use Internet printed pages. In addition, she has to reassured that you are not trying to have her declared illegitmate by your actions, that you aren’t out to disinherit her, etc. And of course, even though she is all grown up- she needs to know that her daddy loves her, her daddy ALWAYS loves her, and he is ALWAYS going to be her daddy (Bring ice cream).