Personally I’d be way more concerned with using OEM Android in the West than using wechat anywhere but if it’s really an issue for you then I’d say insist on trying session or signal… One of those are probably your best options if you’re worried about being spied on…
If she’s unwilling to try them or doesn’t like them then I guess you have to settle for wechat or traditional SMS (although without RCS I find SMS to be a trip to a previous decade lol)
I have graphene OS on my pixel 8. RCS works flawlessly with the Google messages app. No issues…