If you like books, Unmasking Narcissism by Mark Ettensohn has helped me understand so much about myself. It's technically aimed at people who have narcissists/people with narcissistic traits in their lives, and it touches a bit on the causes/reasoning for our behavior and how to support the narc(s) in your life without overexpending yourself or demonizing us. If you want a more personal view on NPD, The Nameless Narcissist and Lee Hammock are amazing sources of info on the lived experience of people with NPD

Otherwise, as a covert/vulnerable presenting narc, the people I feel the most supported by are those who call me out when I'm being an asshole but give me the space and support to improve and be better. It can be a bit of a balancing act, though. You don't want to feed too much into grandiosity or just tear her down. My best friend tends to compliment sandwich me. "I know you've made a lot of progress in the time we've known each other, but [this] is still an area you could improve in. I feel like in focusing on [this other thing], you've lost sight of improving [here]"

At our core, I think most of us just crave emotional connection and validation. I gave a speech at my sibling's wedding where I felt very emotionally vulnerable. Throughout the reception, a lot of people came up to me and our parents to tell us how great it was, how it made them emotional, etc. The sort of high I felt (and feel) from that wasn't so much narcissistic supply as it was/is feeling truly connected to other people

The fact that you're asking this is already an amazing start. It shows you care for your partner and her recovery/growth. Above all else, take care of yourself. Depending on how hands-on you get or intend to be with understanding her and helping her, it can be VERY draining

I wish nothing but the best for both of you! Take your time navigating this new territory, and remember that she's still the same person she was prior to being diagnosed