Kitten urinating on futon

I have a female kitten about 8 months old. She is urinating in the same room on the futon where her litter box is. i just put 2 litter boxes down because i have an older male cat. 

I cannot get the kitten fixed be cause she has congenital diaphragnic hernia which I've discussed in another article. She can't have surgery to or her lungs will colapse. So i'm dealing with her going into heat every couple of weeks but i've been ok with what's been happening except for the urinating. 

I cleaned up the futon using a recipe of household items, viniger, water, baking soda, and hydrogen peroxide. Not sure if i should buy the good stuff at the pet store but i probably will this week the spray the futon down. I just don't know how to control it. If I put double sided tape or tin foil down on the futon to make it uncomfortable for her, she may go somewhere else, which would be worse because i have plastic down and a sheet to protect the futon. 

I just think its her being in heat but this has been going on for a few weeks and so she's been doing this while not in heat.

Any suggestions? Is it because of her heat cylcle or mayber more behaviour?

After I had to put my old male buddy down, I adopted a small female 3 or so months after. I found she was urinating only in places she could smell the other cat. She pee'd in his old cat bed and in certain spots where he had had accidents when he was sick with cancer. Once I removed/cleaned these areas, the problem was resolved in my case.

Have you ruled out a UTI?

Have you tried using kitten/cat attract litter in any of the litter boxes? That would certainly be worth a try.

You will need to get some enzymatic cleaner (Nature's Miracle works really well) and clean the futon EXTRA well. Homemade cleaners work to clean to our standards; but, are unlikely to truly remove the scent that a cat can smell.

If doing the above doesn't help the issue, the problem very likely is behavioral and tied to her being in heat. I haven't read your other thread yet; but, if there is absolutely no way for her to be spayed, it may be an issue you (and she) have to learn to cope with. =\