Rosavellt kept on staring straight at Dulla. Rosavellt knew how unpredictable Dulla could be. Dulla was the sort of hot-headed person that would charge into dangerous situations without even thinking and it wouldn't be a surprise if she tries something stupid soon. There was even a high chance that she would just charge at the demon lord.
Right now, Rosavellt was doing Dulla a favor. If Dulla charged at the demon lord, Dulla would lose. There was no chance that Dulla could win against the demon lord. She would be dead before she even took two steps forward. Rosavellt already lost one member of her family and she didn't want to lose another one.