So tarinai yu gets killed because they are a drain of resource, youmu was told to kill the little sister tarinai but they end up meeting a factory worker and learn specific youmu type are incapable of normal speech. In order to let the sister live she gave the location of the herd and in exchange to be kept/give sister a place she joined in on killing her fellow herd members.
She got her position by betraying the herd which practices euthanasia.
The thing is, the herd's view on premie/ easy yus depends on whether they are capable of speech or not, the little sister youmu here is capable of doing everything an adult yukkuri does except speech, since the herd views yus incapable of speech to be premie/ uneasy, they told the big dister to kill her younger but she's unable to do it.
that was a misdirection final panel on the previous page, i think most of us thought it was a pesticide spray. but i think it was a spraypaint can to spray on the badges