kitten urinating WAYYYY outside her box!

Background..this is kitten no. 2, Angel is 5 months old and is our 2nd cat. The first is about 1 year old. We have had Angel since being weaned and had some issues with her just urinating around the house. We thought it was behavioural and being in a new environment.
She has been checked out by 2 different vets 3 times for UTI but they give her a clean bill of health.
She was good for about a month using the box, then we discovered she had went on one of the beds in our house.
We have kept her in the storage room with the litterbox while we are gone at work and let her out when we are home but back in when sleeping.
after 2 weeks we let her out full time and she was good again for 2 weeks and then this past Monday morning she went on the couch and just sat it in the spot and didn't move!
We have talked about getting rid of her as it is a pain to clean up this mess but one of our daughters has grown attached to Angel and it was devastate her to get rid of the kitten.
Any help or advice would be appreciated it.

How long has she been doing this? How long has she been part of your family? I've suggested this before, but you may consider trying some flower essences. Cat Faeries has some good ones. (http://catfaeries.com/essences.html)

There is a reason the cat is doing this. Did anything change around the time this started?

She has done it since day 1 when we got her at 6 weeks old. She has only done it a handful of times and even defecated on the carpet twice early on. But hasn't done that since thank goodness.
The last 2 incidents have been like 2 weeks apart and nothing in our house has changed. We are afraid to let her out during the day from the storage room where the litter box is b/c we don't want our furniture damaged any more.

I would check out the stickies at the top of the behavior forum and go from there.

have you porvided her with two litter boxes? Some cats just want to use 2 separate boxes for their pee and poo. (Seperate from other boxes if you have other kitties) I had an issue with one of mine pooing ouside the box and adding more boxes completely eliminated the problem, instantly.

Also make sure the litter boxes are always clean.

You have to clean the areas she is using for potty with some kind of enzyme cleaner or she will go back to those spots again because she smells her scent. Natures Miracle that can be purchased and the pet sotre is an excellent cleaner.