Sorry, but this sounds like a bug. If it was presented as quinta essentia in your inventory, she should be cured. Lift curse property with any strength and without kill effect should be enough. Moreover, it should disappear from your inventory after being used.
I hope you weren't disappointed very much. Congratulations for finishing the game anyway.
Replayed the game and got the ending. It is neat :) The game was very fun, though the bugs can be pretty frustrating but that's expected in a 7DRL. The interaction of processes and ingredients is cool, particularly in that there's no limit to how processed you can make something except time. A pretty good strategy seems to be to make an Improves Stat, Fumes, Adrenaline potion (it would be even better if you got it to improve both stats but I haven't done that yet because time is a pretty serious concern. Either stat works but STR is easier) and then just age the heck out of it-- fumes gets better exponentially and even a single point of adrenaline means you can eat the whole cloud. The increase in stat improvement likelihood is also nice if that's in the right slot.
It does seem, though, that if you muck with an ingredient too much it can cause problems-- the game starts outputting error messages occasionally at the very least. The processes are cool in that they do a good job of being thematic given the limitations-- if you boil something long enough/enough times you usually end up with nothing, for example, and rotten food is usually bad. It's a little weird that spoiling is sometimes really good and you can't do that without fermenting first.
Fumes is by far the most powerful ability-- it can multiply a potion's effect by 9 at the lowest levels-- but it doesn't help with offensive potions and it doesn't do anything on its own so that's kind of interesting. Persists is sad-- it pretty much only matters with Fumes and only if your cloud doesn't have adrenaline. For offensive potions it's not really needed because a good offensive potion should be useable in melee and Persists doesn't let clouds get used multiple times (which would be rediculous, admittedly). Persist, however, seems to be pretty buggy-- persist items trigger the bug where splashed ingredients aren't consumed more often than other items.
The limited inventory space really makes Improves Stat items essential. You can't carry very many Heal/Teleport/Paralyze/Adrenaline/Burn potions and each of those solves mostly just a single fight (Heal is better, but the issue there is you get nothing from fights and you will run out eventually) and limits what else you can pick up. Improves Stat is permanent and, at high levels, makes you able to easily cruise through the whole game without taking very much damage even without potion use.
Thanks for the comments. Balancing the issues you mention would cost me very much time though (because of crazy technical debt caused by the challenge's pace), so I'm not planning to fix them.
Still, it's a good game-design exercise to try to think what could make the alchemical processes and effects better. I think that especially improving the fumes' offensive potential would be fun.
