The Perceived Stress Scale and The Ardwell Wellness Stress Test may be appropriate for your needs. They are "universal" tests but can be applied to nurses/nursing. The Stress Coping Resources Inventory: A Self-Assessment looks at levels of stress and coping ability. This may be more what you had in mind and may be useful for your project.
As far as theories/theorists, if you aren't required to use Neuman as a theorist, considered Orem's Self-Care Theory. Her theory can be applied to nurses/nursing. Her concepts of self-care deficit and self-care agency can be applied to nurses/nursing. Stressed nurses have a self-care deficit, and when they are overwhelmed between the demands of working during a pandemic and meeting other requirements in their personal lives they may also not have "agency" to meet their own mental and physical health care needs.