Inviteseller, I'm so sorry that you have to cope with all this. Good for you for being a strong parent for the sake of your daughter, even if it means doing the hard thing and not yielding to unreasonable pressure.
If I were you, I would not discuss it at all. It is not open for discussion, and it takes two to tango. You've already explained yourself, but they refused to listen. So stop wasting everyone's time by trying to explain. Give no reasons, just repetitions of "this isn't your business and I won't discuss it. Please stop nagging me." If it gets worse (as it sounds like it has been from one person), I would say bluntly and honestly: "I've told you that I do not want to talk about this. I've asked you to stop. You keep ignoring me. I don't know why you keep doing this, but it's rude and honestly it's making me dread spending time with you. If that's what you want, that's fine, but otherwise, please give me just a little bit of respect here and stop. I won't ask again." A response of anything like, "but I just want what's best for you and leech, so nag nag nag" should be met with you leaving the room. Cut off most contact, enough so the message comes across. If the person has an ounce of empathy, they'll realise you were serious (since apparently telling them flat out to stop is seen as nothing more than a joke), and will say something to you. You can then rebuild things.
Clueless people aren't always harmless. A person who hurts you and your family is bad enough, but a person who wants you and your family to be hurt is just as bad. And that is what this person wants. They want to risk you and your daughter's safety and peace of mind based on a Hallmark-ideal of what a family should do despite all indications to the contrary. And anyone who wants to risk the safety of you and your daughter is dangerous, no matter their intent. And this is what we have here. Even if no offence is meant, the person is proving themselves to be just as damaging by refusing to listen to you or consider you. Unfortunately, you might have to be very firm.