Sister Needs Help

Guys, I need some advice for my sister. She is 29 yrs old and a mother of 2, very good looking woman, but self conscious about her weight. She has a nice figure but can use a little toning and maybe lose about 10 lbs. She does not work out, as much as I preach to do aerobic activity, she just wants to diet and walk on her treadmill 2-3 days per week. My question is, What kind of diet would you guys recomend for her. I didnt know If I should tell her to go on a cut diet, cause I wasnt sure if she needs all the protein., Any advice would be greatly appreciated, thanks guys