You know I really really like this crossbow. It legit poses a threat to the MC as she will probably expect it to be akin to a bow and arrow, the guy has one shot that she won't be prepared for, it is a really nice way to generate some stakes while still staying really grounded in reality, we're not throwing a second death god at her to put her in danger, or throwing some magic or anything, but having a slight technological advancement she doesn't know about that will get one good surprise attack. Or well it would, but she probably is able to deal a real ballista trained on her and she is straight forward enough that she will see it as a weapon she doesn't recognize and prepare for anything. This crossbow will also gall into the kingdom's hands now allowing them to reverse engineer it.
Also, the carnage Olivia brings, just perfect. Brutal enough to justify everyone, friend and foe, freaking out over it but not brutal enough to be too much for most of the audience. Olivia's take no prisoner's attitude combined with the destroyed morale also fits in with the troops surrendering. This series is just great.