Would it be OP if she took all shadows? If it is, I'd be fine to keep it to just her own shadows, plus the shadows of her chosen target(s). Like - she has full control of her own shadows. She can transform into a shadow and attack like that. And she can indirectly attack someone through that person's shadows. If course, that would mean that the target can't be in a shady place, and she can't attack through shadows at night.... unless there happens to be a source of light nearby.
She won't disappear of course, but she still wouldn't be able to attack their shadows specifically. But she could attack with herself as a shadow. If that makes sense.