For those who don't follow Agents of SHIELD:
Some context: That serum she injects herself with close to the end is a modified version of the Centipede serum, which was a super soldier serum created through a Hydra project. It was supposed to be used to on someone else, but she used it to become powerful enough to save the day. She has presumably kept this amp, as it was meant to serve as a permanent cure for the other person.