At a minimum there seems to be a conflict of interest here if the POA is benefiting, but that doesn't necessary mean it is a misuse of their power. You'd have to show that it is not benefitting your MIL by sending her away.

The other way to contest is to contest the POA isn't valid. Was your MIL still with it when the POA was created? If not, you can argue its not valid and petition the court for a guardianship appointment.