In regards to Minfillia joining Hydaelyn;

The dialogue from the Word indicates Mini willfully choose to join Hydaelyn as she wanted to do something, anything, to aid. "If you can't speak, then let me speak for you!"

You also must remember Minfillia had no idea what we were doing as she had been floating in aethereal sea while we were helping Ishgard.

Minfillia seems more like a sanctified martyr in her current state, verses an unwitting pawn.