Peeing cat.

 I rescued a mom cat and her five kittens. The first day I brought her home she immediately used the litter box, actually quite frequently. At around seven weeks she seemed like she had started to go into heat. She didn't want anything to do with her kittens anymore. I had noticed a puddle outside the litter box. I moved her into a carpeted room upstairs. She used the box and there were no accidents. During her seven week period with me I had changed the litter to a different brand and she seemed to adjust to each change. She was placed in a good home with one of her kittens. She was still nursing the kitten so the person waited to fix her. A few weeks went by and my friend noticed that the bathroom mat was peed on. I myself had visited and  the cat came into my room and peed on my laptop bag and looked at me and meowed. I advised my friend to fix her. I thought she was in heat and marking. She was fixed the next week and everything was fine for about three weeks. Then there was pee on pillows, bathroom mats and a chair. We assumed the kitten was in heat and perhaps following what her mother had done. The kitten was then fixed and it all stopped for a few weeks until more pee same places and new places. Mostly the chair and then under the chair. My friend is taking the cat tomorrow to the vet to see if it's medical. A couple of points that I forgot to make. When my friend adopted the cats she gave them only dry food. The mom would freak out when her kitten came back from the vet and spit at her but then warmed up to her again. They play together and snuggle. When the mom cat peed on my bag the urine seemed dark not clear. I am posting this now because I don't want this cat to lose her home. My friend is a good person and loves these cats and doing everything to help them, but if it's a behavioral, I don't know how she can keep up with it. The mom cats belly has gotten bigger lately and she is fixed and only a year and a half. Would welcome input.

Is the litter box scrupulously clean? And how many litter boxes do you have?
I recently ran into a problem with Ritz peeing outside the litter box, in the first case, in the next room, in the 2nd case, same room, as her litter box. Turned out she was really bothered by the smells surrounding the litter box (pee pad).
I'm glad your friend is taking her to the vets; the dark pee worries me. So does the big belly.

My friend took her to the vet and found nothing. They did xray, blood but said there wasn't enough urine to see. She had an ear infection which she got antibiotics for. So the new questions are, did the peeing while in heat leave the smell on the chair give her desire to go back? My friend did clean it with those enzyme cleaners, but maybe not enough. She still only has one litter box.  

I would again clean thoroughly the chair and other places she peed in--whether she is in heat or not. Unfixed male cats urine is very very smelly strong; I don't know if the same is true to female cats.
Also remember that cats can smell what humans never can.
And get another litter box--they are inexpensive enough.