It’s not only the fight against the assassins, in basically every combat until now (except some goblins she trained on during the travels) she was not in control and usually have to force her skills to perform at a higher tier. Just as an example we have the bandit hunt where she fought the leader, here in the manga it looked like she was in full control and it was over in a couple of panels, but it was actually really close as she had to optimise her stamina and the bandit were really good at aiming for her.
There isn’t much off-time in the LN either, there’s like one arc that’s a bit slower but we’re far from that. Training time is mostly skipped now as she gets more training while in combat.