I haven’t seen this proposed before anywhere. This is an alternative to or addition to existing defiling systems. I have 3.5e in mind but it can be adapted to any edition that uses spell levels.
Here is how it works. Once per day for each spell level a wizard/sorcerer knows, it may cast a spell from a higher level in the slot immediately below that level. Here is an example.
Chidus is a 5th level wizard. Usually he is a preserver, but on occassion he has felt the temptation to defile. Chidus knows 0-3rd level spells. If Chidus chooses to defile, he may prepare a 1st level spell in a 0 level slot. Alternatively, he can prepare a 4th level spell in a 3rd level slot, even though he could not cast 4th level spells. The spells cast this way are not heightened - they are cast as spells of the level of the slot from which they are prepared.
Chidus can do this 4 times a day, once in each slot of 0 - 3.
Another example. Mazrim is a 1st level wizard. Mazrim can cast 1st level spells and he has a deadly duel tomorrow that he is certain to lose. Mazrim prepares blindness, a spell that is in his spellbook but one that he cannot normally cast because it is 2nd level. Blindness is instead prepared in Mazrim’s 1st level spell slot and Mazrim will have to defile to successfully cast the spell tomorrow.
The next day Mazrim fights the duel, defiles the land to gather the energy sufficient to cast a spell beyond his normal abilities, and successfully blinds his opponent and wins the duel. Mazrim feels bad about the defiling, and even suspects that compromising may be a slippery slope, but Mazrim is glad that he is still alive.
I think this accords with the way that Sadira was defiling. You can plug this right into an existing defiling system or replace it with this system.