I agree with BW- if it was a fill in teacher and they were not aware of the situation then they dont know what they don' know- does the school have an action plan for your daughter? A medical condition which involves feinting and seizures should have an action plan, that should be passed on to a fill in teacher.
As for sending a child to take her to the office- they were making the best of a situation, obviously it might have made sense to send someone to the office to get help. Unfortunatley the probably couldnt have taken the child themself as they have duty of care to all the students, and there for can not leave an entire class un attended.

When you speak to your principal I would be asking for some sort of plan to be drawn up, so that if this happens again, they can get her the proper assistance straight away, then everyone who teaches your daughter should have a copy of the plan so they know what to do.

I hope she is feeling better soon.