I think you are confusing Conjury with Succor. Conjury is elemental magic with the environment as the source of aether (in contrast with Thaumaturgy, whose source is the caster himself). Succor is a special type of magic granted directly by the Elementals and, because of that, the only branch of magic that can be actively denied (in theory, anyway).
In other words, your character can go mad (no pun intented) with Conjury as much as you want her to. It is not a type of magic that requires intervention from the Elemental: it's just extraciton of aether from the environment. If she is a White Mage, though, the Elementals may step in and turn her (white mage) powers off. You could maybe come up with ways for your character to fool the Elementals thanks to them being weak after the Calamity, but that might irk some people.
Or, if what Noeh is true about the Elementals not turning off Succor ever, then your character will be subject to the Woodwrath: they basically turn the whole Black Shroud against you if you step in it.
The weak lalafell in the THM storyline is a character who is stated to have a low internal aether level. Basically, the reason he is 'weak' is because he lacks the necessary magical energies to cast spells. Trying to do so could result in death.
As for reasons for your character to go evil...well, that depends on your character's personal story and the best person to come up with that would be you. Just remember that you can have more mundane reasons to steer your character in that direction. No need for fancy evil spirits or artifacts or magical nonsense. Old psychology can work well, if not better.
Aether sickness is a phenomenom caused by the shift in the aetherial flow of the world, something that occurred thanks to the Calamity. You'll suffer it if you are in an area with high levels of aether, though apparently you can get used to it (the Player Character never suffers from it again after the intro). I also vaguely remember it can make certain creatures more agressive, which I guess is a good way to justify all the aggresive mobs in the world. But don't quote me on that.
In other words, your character can go mad (no pun intented) with Conjury as much as you want her to. It is not a type of magic that requires intervention from the Elemental: it's just extraciton of aether from the environment. If she is a White Mage, though, the Elementals may step in and turn her (white mage) powers off. You could maybe come up with ways for your character to fool the Elementals thanks to them being weak after the Calamity, but that might irk some people.
Or, if what Noeh is true about the Elementals not turning off Succor ever, then your character will be subject to the Woodwrath: they basically turn the whole Black Shroud against you if you step in it.
The weak lalafell in the THM storyline is a character who is stated to have a low internal aether level. Basically, the reason he is 'weak' is because he lacks the necessary magical energies to cast spells. Trying to do so could result in death.
As for reasons for your character to go evil...well, that depends on your character's personal story and the best person to come up with that would be you. Just remember that you can have more mundane reasons to steer your character in that direction. No need for fancy evil spirits or artifacts or magical nonsense. Old psychology can work well, if not better.
Aether sickness is a phenomenom caused by the shift in the aetherial flow of the world, something that occurred thanks to the Calamity. You'll suffer it if you are in an area with high levels of aether, though apparently you can get used to it (the Player Character never suffers from it again after the intro). I also vaguely remember it can make certain creatures more agressive, which I guess is a good way to justify all the aggresive mobs in the world. But don't quote me on that.