The Win-Win approach is the most appropriate negotiation strategy in situations where collaboration and ongoing relationships are prioritized. In this case:

Achieving cost savings: The NHS aims to reduce expenses in order to reallocate funds to critical areas, making it essential that both parties work together to find cost-effective solutions.

Collaborative supplier relationship: Since Maria is working with a collaborative supplier, maintaining a positive relationship through mutual benefit is essential for continued cooperation.

Alignment with public service objectives: A Win-Win outcome aligns with the NHS's broader objectives of maximizing resources for patient care, as it ensures that savings are achieved without undermining the supplier’s commitment to quality service.

This approach aligns with CIPS guidelines for maintaining productive, ethical partnerships in procurement, especially in critical sectors like healthcare.