poor choice

There was a very good reason that Grace was saying this to the nearly unconscious Isa. She had looked to Isa for teaching and knowledge. When it came to controlling ice energy and creating things with such energy, she had become somewhat of a proteges. The very same that they had all become when it came to Maria teaching them archery. 

But the reason that Grace was apologizing, was because Isa had warned everyone not to attempt to fuse themselves with their beasts like she did.

This wasn't because Isa was trying to protect family secret techniques or anything dramatic like that. It was much more seriousness.