The Crimson Binome
Hero
If you want to have some agreement about how powerful everyone should make their characters, then that sounds like something you should discuss before the game starts. It's not a matter of role-playing, at that point, so there is no one correct answer. Complicating the situation, Pathfinder is especially sensitive to system mastery by the players - the power of your character is proportional to the number of books you've read multiplied by the amount of time you spend on character creation, so power imbalances can get pretty significant unless you really work to address that.The character doesn't choose their stats, but the player does, esp if it's a point system. The player also chose not to invest *any* resources in defense for their character. It would have been trivial to raise the defenses of the character from non-existent to mediocre - still need to hang in the back line, but not critically weak.
It's not about the degree of impact; it's about the reason for making that choice. Any risk, whatsoever, is unacceptable if there's no good reason to take it. Remember, the lives of everyone in the party depend on how well you perform in combat, and if they die because you took an unnecessary risk then it's your fault and you will have to live with that forever in whatever sort of afterlife you end up in. Probably a bad one.There are tons of in-game reasons the fighter would have picked a scimitar over a long sword. Perhaps longswords weren't available in the area of the world where she grew up. It is a player stylistic decision that slightly weakens the character, but the impact is minor.
If the fighter has never seen a long-sword before, then that's a justified reason right up until the time she sees one, at which point she already knows how to use it and can immediately intuit that a bigger blade is more effective. It's not rocket science. If your character is exceptionally dumb, then you might get away with it, if you have a lot else going for you - if you're playing a literal gorilla, for example, then people might be willing to overlook your inability to figure that one out.
If it's just a stylistic decision to accept an increased chance of everyone dying so that you can use a sword that looks cool, then that's a bad reason and any serious professional will know that you're not to be trusted. Seriously, it's not cool to risk even a .01% chance of everyone dying just for your aesthetic.
There are plenty of good reasons why someone might choose a scimitar over a long-sword, but these are not some of them. These are bad reasons.