I have been watching a friends dog for them for the past few weeks. She's in the hospital. May be for a long time. I go twice a day and let him out and spend some time with him. He loves seeing me, but he constantly stops and looks out the window....waiting to hopefully see them come home.
Her hubby comes home now and then, but the hospital is 2 hours from where they live so he stays for days at a time. So I try to stay and play with the dog each time I come, so he has some companionship.
Maybe you can try to take some time when you come to play with the kitty, that may make her feel more at ease. A laser light, or string (but take string away later so she doesn't eat it). Then she'll begin to trust you and maybe not lash out like that. I'd try that first over the pennies or water. Distract her with a string or light. If that doesn't work, then you may have to use the other methods.
I hope they have a plan for the kitty if something should happen to its owner. Sounds not good.
I hope things work out. Good luck.