Kitten pee's on sisters stuff

We got a kitten that was about 2 months old from a friend. We brought her home and she would pee on my sisters bed, we thought she just didnt know better and that we got her when she was still too young to leave her mom. So we put her in her litter box, rewarded her for using is and washed the bed with vinegar to get the smell of pee out. It has been a month and she is now peeing on anything my sister owns. She doesnt do it to anyone else but my sister. It is at the point that my sister is ready to get rid of her. What can we do to get her to stop peeing on things? note: She uses the litter box all the time and only pee's on things when my sister is home. We have tried litter box training, cleaning the area she pees on with venegar, changing the brand of litter, changing the litter every day. I have made her and our other kitten toys to play with and try to give them as much attention as possible. We changed their food and everything and she still pee's on my sisters things. We do not think she is spraying because it does not have an odor. And I need to drive home that it is only my sisters stuff. She pee'ed on my shirt once but only after my sister had worn it.

First, I'd get your kitten checked out by a vet just to make sure she is totally healthy and not having a medical isssue. I'm not sure why your kitty has chosen mainly your sister's items to urinate on, but kittens and cats brought into any new environment can be very stressful and thus improper elimination is quite common. Think of your kitten as a baby...all she has known in her life are gone. No mom, littermates, different house, different smells, diffferent food, different and scary new people (to her, of course ​)...it's all very intimidating and very stressful to a kitten. This is just one of the reasons why people encourage adopting two kittens at the same time instead of one. Anyway, is your household any different when your sister is around than when she isn't? Cats are very sensitive creatures, so if there is a change in the activity, noise level, etc, your kitty picks up on this right away and may feel distressed especially in those times. Make sure she has a quiet area where she feels safe. Keep her litter box, food, bed, cat tree, water, toys, etc all in that room for now. She needs a place to feel safe and escape from the stressors she feels. Sometimes getting a calming diffuser can help if you cannot change things in the house. Put it in the area your kitten hangs out the most. Try to approach her in a calm manner, and give her slow blinks rather than stares. 

Another reason for the vet exam is that If she is in pain often enough when she urinates in the litter box, she may choose to go to a softer, more comfortable surface like your sister's clothing or bed instead. I'd also make sure any clothes lying around are picked up promptly and put away in the closet or closed hamper so she can't get any access to them. A cheap bed-bug cover (vinyl material) are usually waterproof and can encase the entire mattress for future protection, too. Close te door to your sister's bedroom to prevent further accidents. Some kittens may also be sensitive to the type of litter being used. Can you mention what type you're specifically using right now?

In the meantime, I'd also make sure that you use an enzyme cleaner (buy a gallon of Nature's Miracle, for example) to soak any and all previously soiled items. Vinegar won't break down urine salts and crystals that are left behind, no matter if you even use bleach, hydrogen peroxide, baking soda, or other chemicals and detergents. Urine is just chemically different in that way. Even if you can't smell it, your feline can. A cat's sense of smell is 14 times greater than ours, so if your kitty detects it, she is likely to eliminate in the same spots again.

I hope you get this resolved very soon! And I hope your sister also begins to understand and has more patience. Part of being a new cat-owner means preventing things from occuring, and often includes human behavior changes rather than our feline's, lol. Best wishes to you and your kitten...