How did she get killed by bandits?
Maybe in chapter 2 we will see what the deciding factor was
Because it wasn't bandits but knights/soldiers in disguise.
From what's shown, the deciding factor is simply FL's offer to welcome them in her country.
In the OG she probably wasn't this determined due to not having the alternative option FL set out for her here.
Even if she fought back, won and arrive home, it'll just lead to in the worst case civil war between her family and the rest of the country.
And being a family that guard the border, it's hard to imagine they'll be welcomed by the neighboring country.
But now with FL's offer not only does she has an escape from the country, but her family is also welcomed there, so she can go all out fighting.