Direct report only shows good judgment/willingness to perform when under the gun

It's only when she gets in hot water for performance issues and I start checking out that she snaps out of whatever dumb phase she was in that caused her to be a bad worker. When I say check out I mean be more matter of fact, less available, more economical with my time. The reason being that when her mood is good (and her work is not), her ego grows tenfold, she gets into everybody's business, and none of my coaching/guidance/feedback/Socratic methods stick. None of it. But when she's afraid for her job? Only then will she remember.

Me? I'm only middle management. I can't unilaterally fire or put her on a PIP. I can only document and build a case.

Am I stuck with her until then? Should I find ways to keep her ego in check, so we can all get some work done?