Why doesn't my dog grow? its a 10 month old german shepherd cross husky and looks like a four month old?..?

i have fed my dog chicken, rice, biscuits and many other things in the past she doesn't really like.. now i have recently put her on 'wagg' but she doesn't grow, she is a ten month old german shepherd cross husky and when she sits she is level to my knees, and i am only 5ft 4. how can she be healthy, without changing the food? btw i feed her 4 times a day and walk her every 2-3 days for an hour and half. and she hasnt been wormed till she was six months, but there is no signs of worms, she is just very skinny, thanks for your help..