Wow yeah that works!
We can now see each other in Zerotier, she got to make a card in my Asphyxia network -> my friend can now play in the same network and I can change her custom bgm, spaceship etc.
The only issue now, albeit probably the biggest, is that we can't see each other when trying to match in Friend, SIngle Battle, or just Normal Matching.
I made sure to install our emulators step-by-step the same so we should have the exact same spice and game versions. (I'll be re-installing everything later jic)
Are there other factors that could be preventing us from seeing each other in-game other than version difference? Ty for the time!