"You saw her character."
Translation:Chonaic tú a carachtar.
NB that the word "character" does a double duty in English to mean both one's character as in one's nature or moral core, as well as to mean the roles in a book, play, movie etc. Irish keeps these two meanings distinct and carachtar refers only to the latter kind. So this sentence means only that you know a woman who's an actress and you saw a role she was performing.
If you wanted the other more figurative kind of character there's a couple of different words you could use. Nádúr means "nature" and it's usage maps neatly onto the English sense of the word. Aigne is another that can also be translated as disposition. Finally if you wanted to praise or defame someone for their character, you'd reference their clú or their cáil which both mean reputation.