Weight depends on two main factors,first genetic and secondly the diet. Since you can't do anything about the first,you need to give her a balanced and healthy diet including curd and Banana in the diet. Give just 2 milk feeds using a glass and 3-4 solid meals a day. There's a range of weights for all ages,and weight and height should increase continuously over a period of time in children. If she's active physically and mentally and is eating well,relax.