If her friendship, etc.. means something to you then by all means tell her so.
One of the best ways of doing this is to apologize. I can hear some of the guys here now saying 'AFC', 'AFC' which is utter bullshyt.
I don't mean by saying I'm sorry for something you didn't mean. Say you hope she didn't take it the wrong way, because that's not how it was intended.
But you take a risk of course as well. That she'll claim she doesn't know what you're talking about, then you'll have to explain it.
That could be somewhat uncomfortable trying to explain the word 'cunt', and why you didn't mean to call her one.

If she's got a sense of humor it could be funny. But of course you can't depend upon a womans sense of humor when it comes to this sort of stuff.
But if she likes you enough you can get away with calling her just about anything within reason. Lord knows I've had some crazy nicknames for girls which I wont mention here.
Good luck and let us know how it works out.