From her Wikipedia article:

"Following an injury, Walters received an emergency blood transfusion from her cousin, Bruce Banner, and acquired a milder version of his Hulk condition. As such, Walters becomes a large, powerful green-hued version of herself while still largely retaining her personality. In particular, she retains her intelligence and emotional control, although like Hulk, she still becomes stronger if enraged. In later issues of the comics, her transformation is permanent."

She looks really happy for someone who needs a new suit