Tell her it offends you. Or show that you hate it. (Do it first as you term her as your best friend)
If she doesn’t stop, unfriend her.
Best friends make fun, but they never make you feel down until you need a reality check. Even then, they help you.
Ps – If you are in your teen, unfriending might feel harsh. But a good set of friends is essential for a quality life. And you just need a few good ones, and not a lot for that set. Choose wisely.