You coach a team. You gain their trust by being compassionate, non-judgmental and result-oriented. You get some results. You are happy.
At the same time you are coaching their manager. She starts asking you what you think of the team and what she could do to improve their efficiency. You start using the information you got from working with the team and from the trust they have in you, against them. You start hating yourself for falling into this trap. Soon the team also realizes what you have done.
Additionally, you find your self (and put others) in awkward situations when both you and the manager are having a meeting together with the team. What if you contradict the manager in front of her team? What if she contradicts you?
Do yourself and everybody a favor and decide who you are coaching: either the team, or their manager.
If you are coaching the team, you will concentrate on improving the team "as is", assuming everybody is here to stay (unless told otherwise or unless someone is a true impediment).
If you are coaching their manager, you will concentrate on helping her be the best possible manager for her team. You will also support her in making tough decisions about team members.
In any case, you will be true to yourself and the person or people that you coach.
Also, you will avoid those awkward situations where you and the manager contradict each other in front of the team.