Salaam.
A lot of times, this is said. Even my parents told me as a kid that if I married a white girl, they'd kick me out. Lol.
The thing is, you don't know what the future brings. You'll support your child no matter what she chooses. All parents should and will (especially if they are Muslim parents) support their children's spouse. We just don't think of it yet and we don't want to. But if it does happen, that's when the biggest test comes.
Let your child marry whomever she wants, it's her choice. You can always say no, but guess what, it's her choice lol. Support her, love her, and be happy that she married a man who she loves whether he is a Muslim, Non-Muslim, or about to convert.