Singing as best she could is an action. I think the skill actors must achieve in order to prevent "indicated" acting is to be able to immediately transfer a director's request for a result into an action. The ability to do that requires practice/rehearsal, and not after one has been cast in a production, but practice on a daily basis.
Directors will frequently say, "be angrier," "be more flirtatious," "go slower, faster." These adjectives are results, and an actor can't perform adjectives. Only verbs will produce an action which will then give the director their desired result.