To answer the question: GrapheneOS and a separate profile would be the safest

I appreciate the suggestion, but maybe I should add that I'd like to not have to change up my phone too much. It's a Fairphone 4 running the OEM Android and my preference would be to keep it that way. Are separate profiles like that a thing on stock Android?

If you are both outside of china there really is zero reason (other than preference) to use that piece of spyware.

She travels back to China sometimes, uses it to contact friends and family back home, and uses it to chat with lots of mainlanders here in Canada. For her it's not weird at all.

In fact, she expressed to me that she's perfectly comfortable with the fact that they use WeChat combined facial recognition technology in China for payment processing. When you get on public transit, you can have them scan your face and it will automatically charge you the bus fare. It really skeeves me out, but it's simply not the hill I want to die on in this relationship. I'm crazy about her in so many ways, it's okay with me if we don't see eye-to-eye on digital privacy.