>>36432483This
>>36432433Making mistakes is one thing, but a character that the story is trying to tell us is morally good needs to have their positive traits outweigh their negative ones. Zinnia doesn't have much time on screen, but for what little time she does have, the story tries to present her as being in the right for preventing the researchers from stopping the meteor. A meteor that was going to destroy the Hoenn region and end countless lives, so she could enact her own plan to save the region. A plan, mind you, that nearly blew up in her face since Raquaza didn't have the power she needed to save the region before Mega-Evolving. She nearly killed everyone in Hoenn because an entirely separate universe MIGHT have been threatened by the meteor that was currently threatening her own. She's an incompetent, self-righteous, maniac and the Delta Story doesn't have the self-awareness to recognize her as such.
tl;dr From what little we've seen of Zinnia, there is nothing redeeming about her as a morally good character, so it's difficult for people to like her when she's presented as a morally good character.