Should I stop being friends with someone.. how to tell them?

I have a friend I've known since 7th grade. I'm currently a junior in high school. Ever since I've known her, she's mothered me like I was a kid or something. comments like "be a nice child" '"don't do that" .. etc... (We're the same age.) At first, I tolerated it, but it eventually got old fast. I don't like to be bossed around at all. I would ask her to stop and she took it well, she said she would stop. A week later she kept mothering me. 3 times later I was like "Hey stop I don't like when you do this. " It got to the point Instead of asking her to stop, I was telling her to stop. She won't stop. The last time I told her to stop, I said "Look if you do it again I'm done being your friend, I ask you to stop doing something that bothers me and you don't stop. " Well, she's doing it again. Even my teammates are noticing it, and asking me how I put up with her and that it annoys them and they aren't even friends with her. I'm genuinely done with this friendship, I don't really want to mend it, and I don't know how to end this friendship nicely. We see each other every day, so ghosting her isn't really an option. Am I being too harsh?