New COO clashing with two most important veteran employees

I run a remote e-commerce company of roughly 40 employees and 3 months ago I hired my first COO, young girl who hasn't done it before and who's motivated and is bringing crazy value to the table. She recruited tens of people after she got in the role and she's been managing/growing them nicely, no complaints at all. The whole business is getting a boost as my hands freed up and she manages most of our ongoing projects and let me focus on the highest level strategy. All of that would be wonderful, if there wasn't an issue with two oldest employees on the team - leaders of two departments who feel disrespected by the way she approaches them as she tends to change things in their departments without letting them know even though we agreed on not doing that and she's also pretty rough with them, in a way I've never been. Those to employees are frustrated together and in sort of an open war with the COO, they do their best to keep their cool, but conflicts appear every 1-2 weeks and I'm becoming hopeless. Even though I told her where's the problem, she keeps on being aggressive whenever she doesn't like something and when they see it, they get reactive as they are fed up with her attitude. I see it as a mistake of the COO not being able to understand the way those two operate to be more sensitive towards her intentions with their departments as she operates from a place of power than credibility there. On the other hand, the COO is together with those two my most important team member and I can't imagine letting her go, it would dramatically slow my company down. I'm seriously looking for someone to jump on a call and discuss this situation, it's very difficult for me and I need some fresh perspective. Thanks for the help!