Harriet thinks Henry Woodhouse is her father.

You're 17. You've been in Highbury for many years. Someone has been paying for your education. Someone has recently upgraded your room, and suddenly, you're invited to come hang out at Hartfield ALL THE TIME, even though the very few people who are ever invited there are either very old freinds or family.

Emma INSISTS that you are a gentleman's daughter, even though there's no evidence of that, and no one else seems to bring it up. Why would she think that?

There are other parlor borders at Mrs Goddard's. Why you? What's special about you? Why is it so important to Emma that you don't marry Robert Martin?

What else is she supposed to assume? She must be Henry's daughter.

I think her dad is actually Mr Weston though. I think at the end, he probably offers to come clean, but Harriet decides, "No, you know what? Fuck all y'all. Say it's a rando. I'm marrying Robert."