Why not Emi est une bonne fille? or even Emi est une fille bonne?
English Translation
Emi is a good girl.
Bien in “fille bien” = morally good or of good character (a good girl)
Bonne would typically refer to ability or quality (elle est bonne en maths)
I looked through the examples on reverso, it seems that the nuance is often subtle and could even mean nearly the same thing.
I think this is very good advice.
There are cases in which you may be able to use both interchangeably, but that is generally not the case, even less so when you’re talking about women.
Talking about a guy, you could say:
C’est un gars bien.
C’est un bon gars.
Word order does matter here:
You can’t say: “C’est un bien gars.” and “C’est un gars bon” doesn’t work either.
Talking about a girl, I would only use “C’est une fille bien.”