I don't see it as evil at all. Any animal on my property I don't own is quite likely to disappear, wild animal or domestic animal. That's what fences are for.
If you can catch the roosters, box them up and take them to her. Tell her you found her birds and brought them back so she could keep them home. Ask if she needs help building a coop. If she continues to not confine them, well, free range birds disappear all the time.