I think making a run for the Chapel would be best. IC Parum would want to stay in the relative safety of the fortress, but she slowly she does realize staying there will only make them sitting ducks. If they could somehow reach any survivors outside the fortress and remain relatively hidden, they could possibly use the situation to their advantage the next time the invaders attack. They'd be so focused on beseiging the fortress that they could lead a fighting force to hit them from behind, or at the very least strike them when they least expect it.
Sneaking to the place would be the hard part, but being a light-foot halfling, Parum is pretty good at staying out of sight. I certainly know that she can use her Minor Illusion to turn into something inconspicuous, such as a barrel. If everyone else wasn't such bigguns she could try to do the same for everyone, but alas.