Once she would get infected then there was no chance that she would continue to hide despite being medically treated. Once she would step outside and try to get in contact with any kind of medical help from any Hospital they would directly get to know through their men and then it would not be a difficult thing for them to get hold of her. They must have presumed that since Sasha did not want to come out then they had only one chance which was to force her to come out. Although Aaric could easily point out a lot of possibilities that this plan of black Dragon had and there were high chances that it would fail, still those people went ahead with this and spread that infectious virus.