Interesting.
I think locking it to 4 choices is correct vs just having write-in or top comment dictates because it allowed for the story to still be somewhat controlled. The votes would reveal different information about the mandrake girl (either her personality or her history/abilities) but the main story beats were always going to happen (we'd always get why did she kill the father, that her family and village were killed, that she's been killing any human she finds in the forest since due to being blinded by revenge, and that she was being held by the four robots that were bringing her things who were made by one of her victims). The fact that they are 4 relatively young robots that don't fully have a grasp on things also helps explain why the vote choices at times and even what the vote was on would seem odd as they were still figuring it out.
The join her ending is probably in the long run what can be the most optimistic. Killing or imprisoning her forever likely would see the forest be demolished and the other beings living in it hunted for medicine or due to hatred/revenge. The just setting her free while her imprisonment and what was revealed during it has forced her to reflect on her actions and how she lost herself to her hatred would likely have ended with her dying to a hunter seeing as how she'd already been injured by one leading to her capture and unfortunately moving towards being a better person would include now hesitating so even more likely to die to someone who enters for the sole purpose of killing her (either to turn into medicine or just to kill so lumber can happen or because government seems to be moving towards an exterminate non-humans based on both the original attack that wiped out her people in the forest and the news article). So the five of them working together probably has the best chance.