It seems, for Kira's own protection, she should be behind a closed door, crated or on lead when strangers are in the house. Period. As was said, the price is too high if she would bite someone.
As far as hearing - GSDs have phenomenal hearing ability. My Csabre will jump on the couch, and look out the window barking.....I look and 3 doors away, someone has come out of their house and is walking their Akita AWAY, not towards, my house. A cat crosses the street - and Csabre will alert on it...again this is 3 and 4 doors away - so at least 150 - 200 feet from my front door, with the door closed, with the TV or music playing. It never ceases to amaze me what she can hear....
It is unfortunate that you have to be so diligent with management, but it seems the safest course of action.
Csabre Sch1, Hexe Sch2, SG Bengal, Lynx, Komet, Kira HGH & Kougar v Wolfstraum ~ Ziberia IPO1 ~ ATB Basha, Kougar & Kyra, Fenja, Sch3s, Cito, Sch2, Danger RH & Alice Sch1s ~Kelsey