haha, you guys are all so evil with your rooster "disappearing" act .lol.
If your going to tell her to keep her roosters locked up and she doesn't, wait a while before you make them "disappear" otherwise you might have more troubles with her accusing her etc.
Yeah just tell her. I'm sure shes not going to get upset. I mean she doesn't seem to precious about them anyway.
Even if you can suggest helping building her a small pen to keep them in.