Well...

[ There's a little voice in Kasumi's head that sounds an awful lot like Jack's, chiding her for disclosing her Tragic But Motivational Backstory to some kid from another dimension. But... oh well. ]

She got recruited into teaching other kids with biotics how to use their powers. And it was a way for her to prove how strong she could be without hurting other people. [ or at least, not too badly! ]