A BTech degree in agricultural engineering is very much valuable, and since it is your choice, I would suggest you to pursue it. There are ample opportunities for an agricultural engineering in India and abroad. Agricultural techniques development, crop yield improvement, soil improvement, agricultural machinaries, farm development etc. are some of the fields of an agricultural engineer. There are many public and private sector employers looking for Ag. Engineers. ICAR is the government agency you can target for a research career.

I do not believe that there are limitations for a girl compared to a boy in any field of a career. All the best.