I just had another thought....try mirroring her words in your response to her. This will help validate her thoughts and feelings while still teaching her appropriate behavior.

Like if she says this isn't fair....you could say back to her I understand that you feel like this isn't fair and that's a hard feeling to have. I need you to do xxxx (and repeat your original instructions)

Thank you so much for being there for her...it would be far too easy for her to get caught up in the system. It takes a strong, caring person to undertake this task. Even experts are sometimes nervous, confused about helping a wounded child. Stay strong and just do your best. In the end, your caring and interest in her as a unique individual will be more than enough.