The Green Party of Minnesota had to begin its petition process for ballot access well before the national party nominated its presidential & vice presidential candidates, so they used Hawkins' name as the VP candidate on the petition. There was no legal process to substitute the name of a candidate on the petition, so the Green Party was unable to substitute Hawkins for Baraka once the latter was nominated.As for what would've happened had she won Minnesota,
Minnesota law specifies that faithless electors' votes be voided & cast for the nominee whom the electors are pledged to back according to the ballot, so had any of the Stein electors cast their VP votes for Baraka, said votes would've been voided & cast for Hawkins instead, which (in this alternate universe) probably wouldn't have mattered much had she
only won Minnesota, but had she somehow managed to win enough states to put her at or above 270 EVs, & the lack of Minnesota's EVs were to bring Baraka below 270, then the Senate would've had to hold a contingent election for VP in January between Baraka & the 2nd-placed VP nominee.