I completely agree with you. FL did make the right choice. People forget she grew up as a sheltered noble lady, yet she managed to survive on her own for years living like a commoner, with nothing and no one to rely on, all while raising a child. I’d like to see any other noble lady pull that off. That alone proves how capable she is.
And honestly, it’s perfectly normal for her to be paranoid. She literally saw a burning pyre prepared for her, heard the assassin claim it was her fiancé who ordered the kill, and then went to his house only to get told the engagement was being called off. What normal person with a normal IQ would stay after all that? Anyone would run for their life.
Plus, she had no way of knowing who to trust. Even if ML wasn’t guilty, how could she be sure he wasn’t manipulating her? How could she risk her life and her baby’s life based on blind faith? She chose caution over naïveté — that’s not stupidity, that’s survival.

Y'all say FL is stupid, but while it was frustrating to see ML get misunderstood when he's so perfect, I personally think running away for 5 years was the best decision at the time. It's better for the son to grow up first before returning to that place.
Even if she trusted the ML and didn't believe he was the killer, it would've taken too long to figure out that the culprit was the sister and something bad would've happened by then if FL stayed close.
ML himself couldn't trace the assassin back to his sister after 5 years of investigation. How would they have figured out in time before FL got hurt or killed if she stayed?
If FL stayed there while she was pregnant, the poisoned tea would've caused her a miscarriage by then. If FL stayed there and she had a vulnerable newborn baby, they easily could've killed the baby son by then, there's secret assassins and servants under the sister's command without even the ML knowing.
Even if FL stayed away from the ML's house, FL's own sister in her house was a traitor too. FL's brother even asked her to forgive the traitorous sister even after making her suffer for 5 years, so he's not reliable either.
IN THE END, FL was ultimately the one who figured out who the killer was, FL was the one who saved her own son, FL was the one who defeated Margaret.
So really, relying on herself turned out for the best. That's why I don't believe FL was wrong for running away. If she misunderstood ML, then it was just the unfortunate outcome of fear and manipulation she experienced by almost being assassinated.
I don't believe FL is dumb, because she saved her son, defeated the villain, and got her man back. I think she did pretty well, and obviously ML was really good too for holding on.