10 month old is only 7.2kg (about 15.8lb), but she just won't each much food?

When you start food, baby does not accept it easily; breast fed is much convenient for baby than food. You have started wrong, might you fed your baby if she refused after one or two bites. Do not offer many times (3 - 4 times meal & 2- 3 times milk are enough in 24 hrs). If she refuses, leave her hungry, next time of offer she will take more bites then last time. Maintain a gap and do not offer anything between those gaps. It is hard for a mother but believe me; it will improve your baby's eating habits.