The RPG Brainrot ZoneTM

- If she'd had a massive quantity of lyrium, she wouldn't have needed blood magic (reminds me a lot of how they need a ton of lyrium and the Circle mages to help Connor if you don't go the blood magic route in Origins).

- She's had the first shard and has been studying it since the beginning of Origins; she herself figured out that it could be cleansed in the first place.

- She asked Marethari to help her initially, and Marethari's refusal was what led her to needing more power to do it alone. Audacity taught her how to cleanse the mirror with blood magic, but it's more than likely she knew the spell she used before contacting him.

But as for the details of the spell, how it worked, why it worked, where the taint went when she removed it (because it couldn't just disappear, could it?), how it didn't infect her, whether this could be repeated or even altered into an actual cure that works for people, we have no idea.

It's fun to be able to theorize about it, but having some more concrete information would be very useful right about now as I'm writing a fic where Hawke and Merrill try to use her spell to remove the taint from Anders' blood (after watching Anders suffer during the Legacy DLC). I've been stuck on the logistics of it, trying to make it believable from a canon perspective (Anders' reaction to Hawke learning blood magic in order to cure him and Hawke persuading him to give it a chance also took a while, but I got there in the end).