First of all, that would still be their fault because they didn't do due diligence on her before putting her on the biggest stage imaginable.
Secondly, she was explicitly chosen because she would appeal to the religious right. They might not have known how exactly batshit she was, but they knew what she represented and they liked it.
Some of the people responsible for this decision are Steve Schmidt (Lincoln Project) and Bill "I love the Iraq War" Kristol (Republican Voters Against Trump). Like, they explicitly advocated for her for that exact reason.
If these people want to temporarily climb aboard to get rid of Trump, then I'm happy they're doing that but I have no illusions about them being good people and have little doubt that they'll be back on their bullshit the second Trump is defeated.
Also, they're still Republicans so they're still going to be all 'fuck poor people, destroy medicare'.