Does a Power of Attorney in MI have the "duty to inform and consult with family members?"

johanna, your Mom choose your sister for a reason to represent her as her Power of Attorney. The sister can do whatever she feels is in the best interest of her [and your] Mom.

If you feel that your sister isn't acting in your Mom's best interest, then set up an appointment with an "Elder Law Attorney" and ask about Guardianship. Be aware that Guardianship is quite expensive to obtain.

https://www.agingcare.com/articles/how-to-get-guardianship-of-elderly-parents-140693.htm

Her actual fiduciary duty is to maintain your mother's privacy, POA is not a democracy.

https://www.agingcare.com/articles/power-of-attorney-explained-187545.htm

https://www.agingcare.com/articles/things-you-can-and-cant-do-with-poa-152673.htm