How do I apologize to my mother after I indirectly called her stupid?

I'm a 14 year old girl. My parents had an extremely ugly divorce when I was 11 and my mother claims that my father had done her wrong so much that I shouldn't even love him. But he is my father and I'll always love him. But what happened was, I put a status up on my Facebook account where my mother can't see what I write. I wrote: I miss my father but of course I can't tell my mother that *grumbles about her stupidity*. Someone from that is a friend of mine and my mother's told her what I had said and she took it as me directly calling her stupid. How should I apologize because she is clearly mad at me right now?