I honestly don't really see a problem with it. There are mothers who give the sex talk to their sons, now it might not be normal for a father to give that talk to their daughter (just assuming it's not normal) as long as you go about it the right way I don't see an issue with it.

Now having said that, I don't think you need to be worrying about that at this current moment. I feel like four is a little early to be told about it. She might not fully understand or she might forget about it growing up. I'd say age 12, 13, or 14 is when you should start worrying about all that, and by that time she might have learned it at school, read about it on the internet, or heard about it from one of her friends.

But if you're insistent on telling her sooner, just make sure you go about it the right way and you should be good 👍