Lucy sounds like my Lakota. Rather than correcting her after the fact I try to nip it in the bud. Whenever I see her posturing or giving my male the hairy eyeball I get her attention back to me. She will guard toys, bones and people. There are a lot of things you can do but I don't really believe the behavior goes away. Management and prevention.
Lakota - WGSD 1/13/10
Wolfen - WGSD 12/31/14
Bull -WGSD 2-10-10
Apache - Shiloh Shepherd 12/15/02 - 6/9/15
Kiya - Shiloh Shepherd 5/15/04 -12/19/25