What are your thoughts on INFJS?

I am an INFJ trying to learn more about ISFJs from other than chatgbt & Google. I recently found out my best friend is an isfj not an infj as she was originally typed as. However the more things happened(danger through people/things) I realized she wasn’t seeing the same lens that I was. Bonus Question: I was wondering how do you know whether someone is not who they seem to be? Please be fully honest, Yes I can take it.