"Une femme agit seule."
I don't know. "A lonely woman acts" would be "une femme seule (or "esseulée") agit".
You mean in a sense of "looking/appearing lonely," right...? I'd say: La femme a l'air solitaire. Frankly, I doubt anybody would ever use the sentence we just went through in any context. This has to be some computer-generated nonsense like many other sentences. Google can't find a single sentence like that.
you miss "acting" "agit" is not translated by "is" but by "is acting" = continuous present of verb "to act" In French there is no continuous present, so to simplify, Duo generally translates the English continuous present by the French simple present: "elle agit" = she acts or she is acting.
"is" is not synonumous of "acts". "is acting" translates in "agit" or "est en train d'agir".
I think that Duolingo is great for practice, but when it comes to really understanding the nuances you must rely on additional sources.
In this sentence, it appears that "seule" is an adverb modifying the verb "agit", yet it takes on a feminine spelling as if it were an adjective modifying the subject, "une femme." Is this the rule in French, that adverbs take on the gender of their agent nouns?
No, adverbs are by definition invariable. In this sentence, "seule" is indeed an adjective which needs to agree with the name but it is "une apposition" and to make it very clear, it would need a comma before:
- une femme agit, seule.
What it means when he or she acts? Is this film-role when actors plays-acts? sorry I am from Slovakia, and my english is sometimes bad.