No, here fort is used as an adverb, not an adjective (loudly=fort) and adverbs are invariable, they don't form agreements.
Secondly, even if it were an adjective, you would only make the noun/adjective agreement when using the verb "être."
Il est heureux. / Elle est heureuse.
Il est grand. / Elle est grande.
I feel a little ambiguous with the adverb "fort". Yes, it is clear in this sentence that fort means loudly, but somewhere in this course fort has some different meanings such as "strong" or "hard": "Le vent souffle si fort" in Weather 3, and sentences like "Je t'aime si fort"... And it is hard to distinguish between fort and fortement, when should I use them?