First and foremost: I totally agree that ST should have included the capability of restricting access to other users.
AFAIK they said that it’s on the roadmap, hopefully sooner rather than later-
There are some work arounds/ other ways to get around this issue that allow you to remove access to the app.
Depending on your router, you may be able to use DD-WRT instead with a virtual presence detector. Basically when the phone is connected to wifi her presence would show home.