I am 22 girl, 48 kilos and 160 meters, i gain weight in my hips and thighs, how much weight i need to gain in order to gain weight in my face ?

~15 lbs: In most people, buccal pad of fat, rather than muscle, makes the face look fuller. Face is also last where u gain fat, as different people add more weight preferentially to different places. If you gain about 15 lbs, that will put your BMI closer to 21, ideal range for you. BMI is just one method of calculating ideal body size, as it differs individually, depending upon musculature, age etc

Weight distribution: varies with each individual, and if you were to gain weight, there is no guarantee that it will fill out your face but usually it will to some extent. If you were to weigh up to 62 kg, your Body Mass Index would still be under 25, which is considered the top value for healthy weight for adults.