Rose pretty clearly didn’t want Pearl sacrificing herself all the time, Rose’s power is a shield, there is literally no reason for Pearl to keep putting herself in danger (except for Pearl’s self-esteem and her belief that Rose is too important to be in the battle at all).

So just imagine a time when Rose gets hurt trying to reign in and protect Pearl. Imagine it’s the only time Pearl has seen her have to regenerate. Imagine Rose hoping it will help Pearl see that how she fights doesn’t help anyone, but Pearl taking it the completely opposite way and internalizing more self-hatred and believing that if she just fights harder, she can protect Rose from ever going through this again. Imagine how hard Rose works to change her mind.