Resident female Siamese not eating since new kitty

by Judy
(USA/ NC)

We rescued a snowshoe kitten 4 weeks ago and she is still isolated in our back bathroom/bedroom. Our resident 10yr old female has pretty much stopped eating both her dry and wet foods. The only thing she will eat are treats. We have tried every brand of wet food out there and a new brand of dry. They have not met face to face yet but of course the resident knows she is there. We have tried different plates and feeding her in a different place...nothing seems to work.
I know she is manipulating us and is angry about the new kitten. She has lived with other cats before with no problem but has been an only cat for about a year.
Any ideas on how to get her to eat? She is always near me during the day...just sits and stares at me. I think I am glad she can't verbalize what she is thinking? lol