She didn't have a power in the first Pulse, most of the characters didn't. I had always considered giving her a power later in some kind of accident. My other options for a power were to make her a battery (and one of the people they'd fight against), or to make her mimic (shape-shifter).
Something about this just seemed to really fit her.
My reasoning here was that I didn't want anyone to be too powerful. The cast so far are either on the lower end of the power scale, or have some kind of problems. Also if I ever wanted Grace to be more powerful, it's an easy choice what improves.
Will we be getting back to the main story arc anytime soon? As I recall, these are all replacements being trained to replace the original superheroes killed in the introduction, and the perpetrator is still at large.