A divided convention could bring in another person if they could not decide on one of the current crop. They would be allowed to do this because the courts already have settled decisions stating that the political situation needs two parties in any race, i.e. Lautenberg in NJ.
Just because she says no doesn’t mean the limelight of history would not beguile her.
I believe that this is confined to 'some' states including NJ. In Louisiana and California, the last two candidates are the top vote winners, regardless of party! This is apparently allowed by that LEFTist-decried doctrine of Federalism.