Step Daughter issues?

I have a 9 year old step daughter. I am having problems at the minute as she doesnt seems to be able to remember her manners! She lives with her mum and comes to stay with us every fortnight for 3 days then stays once during the week. Her rudeness at the dinner table and lack of manners is really getting to me now. I have spoken with her dad about it and he just says to keep telling her. Sometimes he doesnt even notice which then makes me look like a nag. Any advice anyone?