There was another codex about how some guy sacrificed himself to save his lovers life through blood magic. Which is odd if you think about it because whenever blood magic has been an option in game you can only heal your own wounds by stealing someone else's life force but not heal anyone else and conventional healing spells won't work on someone using blood magic, so it would seem strange if using blood to fuel your magic allowed you to heal anyone else. So this is an area where there seems to have been some backtracking from previous lore.
No, I think the blood could have been used to infuse the target with vitality. Sacrificing one's own vitality to restore another person's. Like the opposite of the Origins spell to steal life from a team mate. Either that, or the blood was used for a spell that shielded the target from a deadly occurrence.
Still, if a blood mage is using their own blood to heal the wound, that simply means their own blood is fuelling the spell as opposed to another sacrificial victim.
It's possible she used bloodmagic to power a healing spell, but Solas said that she shed her own blood to close a patient's wounds. It implies that the blood left her body and entered the patient's.
There is no reason why that would give them any control over their patient unless they combined their blood magic healing spell with a mind control spell (which is what blood magic is more generally known to be used for).
Correct, though I tend to think of this as more of a... "infection" of sorts. Like in Dracula lore. Once the blood is inside the host, that blood can be manipulated to take over the host.
So whatever Flemeth did to heal the Warden did not give her control over them. Besides which, she says that her form of possession cannot be forced on the unwilling (which would I assume include mind control)
Why would you assume that? Those two things aren't the same. She wouldn't be possessing the Warden, she would be controlling his mind. Same as she can control Morrigan if she drank from the Well, but she does not possess her.
so for her to control another person would require their consent.
That isn't the case with bloodmagic though.
In the case of the person who drinks from the Well of Sorrows, they gave it when they voluntarily decided to drink.
But they are not possessed. They are under a spell, as would be the case with someone under bloodmagic.