I believe the best course of action is to talk with her FREQUENTLY about what would make a difference to her. If she's a good employee, then you don't want to lose her. However, maybe she feels like she needs to meet some kind of expectation that is higher than what is really expected of her by management?!?
Make certain her goals and objectives are clearly defined and that she understands it is not her responsibilty to "clean up the mess" of others. It is also not her responsiblity to simply do everything that needs to be done, but rather let management know of these tasks so they can be assigned.
Communication is key in letting her know you care and that you want to work with her to keep her with your organization.