A 28-year-old female graduate student with generalized anxiety disorder has been in therapy for 6 weeks. She reports, 'I have tried everything to stop my anxious thoughts, but the harder I try to push them away, the worse they get. I feel like I cannot start my dissertation until this anxiety goes away completely.' She has previously tried traditional CBT with limited success, noting that cognitive restructuring 'felt like arguing with myself.' The PMHNP decides to use an Acceptance and Commitment Therapy (ACT) approach. Which intervention BEST targets this patient's core difficulty?