Weight gain for freshman girls - athletes or not - is very common. Heck, the "Freshman 15" was a thing even when I went to school way back in the dark ages. And yes, I know that freshman boys also gain weight, but this is DFP, so...
My daughter, who has always been thin, put on ~20 lbs freshman year mainly from eating more and weight training. Don't think it was all in the fall semester, but a lot of it was. Exactly what she needed, truth be told. Still has her speed plus now a bit more power. Now, I would not want her putting on 20 lbs every year (we'll leave that to her old man) but as she matures and learns how to train and eat and maintain what she needs to perform at her best, she'll be fine.
My daughter, who has always been thin, put on ~20 lbs freshman year mainly from eating more and weight training. Don't think it was all in the fall semester, but a lot of it was. Exactly what she needed, truth be told. Still has her speed plus now a bit more power. Now, I would not want her putting on 20 lbs every year (we'll leave that to her old man) but as she matures and learns how to train and eat and maintain what she needs to perform at her best, she'll be fine.