Hello, Susan and welcome.
My name is ***** ***** it will be my pleasure to assist you.
I'm sorry you're experiencing this problem with Phoebe.
There are several possibilities for this behavior. Phoebe may be 'marking her territory' to let the new kitty know who's 'boss' and to assert her dominance in the house. The fact that she's just staying in the chair where she pees is a little odd, as cats, as you know, are very fastidious and don't like to lay in their own waste; however, under the circumstances, she may be 'guarding' her favorite chair and making sure that the 'newbie' can't lay in it.
Another cause of this behavior may be that Phoebe has a urinary tract or bladder infection, and she's avoiding the litterbox because she associates it with the discomfort she's feeling. She may be 'leaking' or dribbling involuntarily on the chair and is stressed by the new kitty and is staying put, not getting off the chair.
It's best to have her evaluated by a vet asap, to see if she has an underlying medical condition affecting her urination, and because she's a senior kitty at age 8, she's also more prone to develop diabetes, hyperthyroidism and kidney disease, all of which can cause excess urination and excess drinking. The vet should do a routine senior blood panel, including a thyroid test and a urinalysis.
For the moment, I would remove Phoebe from the chair, so she doesn't get urine burn on her skin, and try to clean her up so she doesn't smell--you can use cat bath wipes, sold at pet supply stores, so she's as least freaked out as possible, as you won't be able to thoroughly bathe her right now. You want to keep her as calm as possible.
Get some Feliway plug in diffusers, which emit a cat calming pheromone and this should help both kitties feel less stressed in the new introduction situation. Here is more information on this product, available in pet supply stores and online:
If you didn't gradually introduce Phoebe to the new kitty, it's not too late (after you're sure she's well, medically), and this site has some very helpful tips and techniques which you can use at your discretion, depending on how long you have the new kitty:
I hope all will be well with Phoebe and the new kitty!
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