For as blood thirsty as Garnet seemed when they found her escape pod I don't think she'd be down with cold-blooded murder. Hell doing this is more likely to make Garnet think Pearl is too unstable to be around Steven, she might just straight up poof and bubble Pearl to keep her from hurting herself and others.

And this is why we need Steven to redeem her before the gems get to her. And what the hell has Peridot done to deserve death? And are we all ignoring the fact that she called for help to get off earth?

We know little to nothing about Peridot and Homeworld. The way I see it, she'll more than likely live because Steven would NEVER talk to the Crystal Gems ever again if they killed any of the Homeworld gems in front of him or behind his back.

Steven doesn't see the Homeworld gems as enemies, he just sees them as gems. And if there's one thing Steven is good at, it's reasoning and lecturing. There's still hope for redemption.