I mean, implying that a woman would only go to the gym to make herself attractive is kind of an asshole thing to do, I don’t think dropping your line would’ve changed her mind

Marriage system was kinda lame in Skyrim imo. It isn’t even that Serana rejects you, she’s just not one of the three or so random NPCs that you have little to no reason to interact with besides attempting to marry (exception for Lydia), so you can’t even try.