I would try to be as honest as I could while trying to be as neutral as possible.

I had a similar situation with my oldest daughter and when she turned 18 she sought her father out and they are very close now. As he got older he regretted not seeing her and wanted to make amends.

Honesty in entirety is important.

It is neither her fault nor yours that her father has shown little interest. Simply answer her questions honestly and directly as you yourself would like to be answered and be sure she understands it's not her fault and try to draw her attention to more positive things. Trying to sugar coat the truth is only going to result in her finding the true truth later and possibly holding resentment towards you for the lie.

Example:

"Why don't I have a daddy?"

You do have a daddy he lives in Mexico. You have a mommy right here though and I love you very much.

You have not lied, or dodged the question nor have you created any illusions such as he loves her because hell, he may not, you have then redirected the conversation to a positive note, you are here and you care. That's what matters.

Well, find a way to keep in touch with her father or her father's family. The reason is clear. It's not a matter of IF your child wants to get to know him, it's a matter of WHEN. You don't have to push, just ask the family to let you keep their addresses should she want to write him when she gets able to write letters. He might find his heart melting when he receives letters from her with pictures, etc. Don't tell her she cannot have a relationship with him, or you will alienate her from YOU. Let her find out on her own, and do your best to help her with all the tools at your disposal (his address, his parents mailing address, a sibling, a family member). In her letters she can send her telephone and email & addresses to him.

Note of caution: Be sure to keep logs of everything that has gone on in the past and present in a diary. You don't want him to contest custody one day out of the blue. If you keep logs you can pretty much prevent him from being able to gain custody. A simple diary concerning the things he has told you about how he does not wish to have anything to do with the child is sufficient, but in your own handwriting, and dated. This is just to protect you and your child, as a precaution. People make mistakes and say things they later regret. He may do this later on.

Enjoy your life with your child and give thanks that there is not the stress of a split with going back and forth between parents. Trust that your child knew what she/he was getting into when she chose you as a mama. If a bond between the two is to ever happen it will at the right moment in your childs life! Trust and enjoy your life. Tell your little one that we are all in the right place at the right time in life and if we are to connect with anyone it will happen in perfect timing. Be confident and do not have any guilt!