What is average height/weight for a 14 year old girl? Does 111 lbs make sense for a 5' 1.5'' girl? Thank you!

Sounds just fine. The average weight for a 13 year-old girl is about 100 pounds (range: 75-145), for a 15 year-old girl is 115 pounds (range: 90-165), and for an 18 year-old girl is 125 pounds (range: 100-175). A healthy weight depends on a girl's height (genetic trait), her body build (genetic trait), and her proportion of fat and muscle (influenced by diet and exercise).