I feel like Nadier might not be the best at the helm, although I may be mistaken. Miara seems like a nice curve into Numa, as well has some decent card draw. I would suggest trying both commanders, and seeing which one your girlfriend would like better. If she leans more towards the Nadier route,
Reyhan, Last of the Abzan and
the Ozolith might be good inclusions, as well as other +1/+1 counter synergies. If Miara is leaned into more, I would suggest more 'aristocrat' like effects, as well as more sac outlets for that juicy card advantage that Miara offers. Things like
Species Specialist,
Blood Artist, and
Rhys the Exiled would be great as part of a Numa + Miara combo. Hope this helped out in the deckbuilding process, have fun brewing!