Dear niece,
In this world you can find people of every kind. Most of the people hide their shortcomings by making fun of others. They themselves suffer from inferiority complex. Don’t worry about that. Ignore as much as you can because if you get serious on that they will continue. You show exemplary moral behaviour and the people would ashamed on what they do. One more thing in order to look healthier you should consult any physician who could tell you how to gain weight according to the height.