I am having a really hard time with dd lately. She has a really bad attitude, not what she says but how she says it. She speaks to me like I am a piece of muck, won't help round the house (which she used to do) without a big row and threats, is unkind to her younger brother, tuts and eye-rolls when I say anything she doesn't like. She won't say she loves me any more. She just wants to lie around and read or play games. This evening she turned round and waggled her backside at me when I told her to get out of bed and brush her teeth properly, and then when I was speaking to her (quite calmly and rationally) about her behaviour started humming and tapping and eventually laughed in my face whilst I was saying how much she had upset me. It all sounds so petty but when she does this every time I speak to her it is really difficult to cope with.
I am ashamed of myself, I called her a little cow when she did that. I have never spoken to her like that before as I always try to treat her with respect and stay calm. I did apologise later for saying that but I know it was wrong. I just can't take the total lack of consideration or love from her when she means so much to me. I have no idea how to get her to stop this. I have tried reasoning with her, telling her off, threatening her with loss of treats/activities, but nothing works. I can't live like this for the next ten years or so until she comes out the other side of teenagerdom 
Any help welcome.