Well you likely kissed her already in the past and you had yeast then most likely so she should have yeast also. The thing is, not everyone’s bodies have a perfect environment for the yeast to become pathogenic like we do, so if her immune system is compromised, then it could be a problem. Is her tongue white and does she have any symptoms really? Have you guys been together for a long time?
She only needs to be treated if she has symptoms such as oral thrush and rectal itching, etc. Otherwise her immune system hopefully is strong enough to fight it off regularly.