How? Her choices about the Earth were largely selfishly driven.
Had she acted as Pink Diamond, she could have set their world free without the war, she said it herself that the Diamonds wouldn't care.
The only reason they wouldn't listen is because she beat around the bush and kept acting like she just wanted out of the responsibility.
So instead she pretended to be someone else and created a needless war and made thousands maybe even millions of gems die and/or be corrupted for what no feels like no reason.
It seems like most of it was just done that so she could get away from her sisters, it was selfish and a cowardly.
There's even evidence she may have purposefully misshapen some of her gems to get more on their side,
The only redemption she might have had was when Greg came along, because rewatching it more it really seem like she legitimately loved him and she was beginning to feel horrificly guilty for what she did as apparently she felt like she should confess everything to Greg,but he may not have let her.
But it's always confusing and hard to tell how much of Rose's love for Greg/Steven is tied to love for them, or some infatuation she had with humanity. (It gets weirder when you add the Human Zoo into account.)
But then Rose giving birth to Steven can also kinda be seen as a selfish jerk move in itself.
She left Pearl alone and confused with no closure and no Diamond.
She left Garnet in control of a group that was entirely Rose's responsibility.
She left Amethyst with no answers about what happened during the war and where she was from.
Note: The Crystals gems never even told Amethyst anything, I find it a jerk move on everyone's part
but it was probably Rose's idea and Pearl is forced to follow orders from her, while Garnet respects her wishes.
This is shown when Amethyst is shocked when the ruby reveals "Rose shattered Pink Diamond."
She left everyone with emotional scars and impossible shoes to fill,
most of all Steven, and despite knowing what would happen to her she didn't explain this to anyome except possibly Pearl.
Again it is obvious she loved Steven, but sometimes it seems like a lot of that came from Rose's desire to be part of him, not just a human being, but a human being free of the guilt that had been tormenting her for thousands of years.
Rose was a selfish person and that never changed, she may have regretted her actions in the end but she never made enough of an effort to fix those mistakes instead she kept trying to escape them.