It's just my guess, no spoilers.
She most likely was caught, interrogated under duress, tortured in order to get information about the other witches, which she might gave out, at some extent at least. Then, likely, she was given a chance for redemption on a terms of public condemnation and leaving the ways of witchcraft, which she had to accept as alternative to execution. The combined effects gave her such crippling mental trauma, so now she has to constantly smoke her special "happy dream" medicine to ease her mental pain just in order to stay borderline functional.