I have no idea how heavily edited the questions are on Ask A Manager, or whether the "reader" is an actual person or a contrivance, but let's assume it's real.

I have no idea how heavily edited the questions are on Ask A Manager, or whether the "reader" is an actual person or a contrivance, but let's assume it's real. Although the "no leverage over her" language is misguided, the fact is that among the duties of a manager is laying out the expectations for a role and finding the right incentives to motivate workers to reach or exceed those expectations. And in this case, the manager is having trouble finding the right incentives because the compensation lever doesn't seem to work. So the manager could spin their wheels trying to come up with lots of creative alternate incentives that may or may not work ... or they could start to chip away at all the things that make it hard to get rid of a person who isn't meeting expectations -- work on documentation, spreading knowledge of their duties around, researching whether a temp agency can help, etc. Or they could adjust their expectations. Which is not to say that it's totally unreasonable for someone to take a month's unpaid leave. The manager should also address the organizational stuff that keeps that from being an unreasonable expectation.