This branch of logic is certainly controversial.
However, that said, if it is applied:
Removing YOURSELF from her life would be a much more powerful incentive than removing her allowance - if you're looking for leverage to manipulate her "bottom."
Alcoholics will continue to drink until the pain of drinking exceeds the pain of doing what it takes to stop drinking. And they can have a very high pain tolerance.
Partners of alcoholics will continue to ponder how to get the drinker to stop, until the pain of staying with them exceeds the pain of leaving them. And they can have a very high pain tolerance.
It's actually deceptively simple. But seems impossibly difficult.
CLMI