How do I tell a new friend I'd rather wave than hug?

At our third coffee, my new friend opened her arms as soon as she saw me. I hugged her because it seemed easier than stopping the greeting. I'm not much of a hugger, particularly with people I'm still getting to know.

She is warm and generous, and I don't want the next greeting to make her feel that I regret becoming friends. But waiting until she is standing there with her arms out feels increasingly awkward. I've also made it look as if this is a greeting I enjoy.

Would you mention it in a message beforehand or say something in the moment? I want to change one small habit without delivering a speech about personal space or making her friendliness sound like a fault.