Senior cat urinating - again

About 1 1/2 years ago, I adopted out a female senior cat (the vet
estimated her to be around 12 years) whom I had found outside in the
dead of winter without food or water. Star had been at my house for
about 6 months before she was adopted, where she never left 'her' room
after the realized I have other cats, though she was not aggressive
when they came to 'visit'. She was adopted into a household with
another senior cat, and shortly after arriving started to urinate in
the house. Vet visits showed no physical indication. She simply seemed
to dislike the other cat, so new owner kept cats separated and all was
well. Resident cat died late last summer, so Star was given access to
the rest of the house. No urinating incidents between September of last
year and January of this year. Then she started urinating again -
mostly on the sofa and carpet in the living room. She spent a couple of
weeks back in the laundry room for re-education, and used the box
diligently while there, so I find it likely that the problem is not
physical. She was let back out into the living area a week ago, which
immediately resulted in a new spot on the sofa. Owner wants to return
Star to me this weekend. Given her age, I don't really want to start
her on tranquilizers, especially as my experience with them is more
successful in multiple than in single-cat households. Would it be cruel
to let her live out her life in the laundry room (which has windows as
well as a screen-door to the backyard) with time out both in the
morning and evening to socialize under close owner supervision, if she
is willing to keep her under these circumstances?

Thanks, Petra