Hi, Mocha,
I agree totally with BB, though I will admit I am not ready for you to give up on your cat, but if you have to rehome her, BB makes very good points to consider.

It is important that you have a local therapist to turn to with your current situation. I absolutely agree that a phone session with the one you know and like is the best step to take immediately. She knows you, your family dynamic, and what you need to do asap to cope successfully with this unexpected issue. You just need some support and guidance, and it may even be necessary for your therapist to get on the phone with your mother and tell her what you need to do to take care of your own health right now. It may or may not involve keeping your cat, but it definitely needs to be clear to your mother that you need to be cared for properly. Once that is put into motion, I think (as much as a new therapist is difficult to adjust to, especially with OCD) you need to get a good recommendation of a colleague from your former therapist, have her contact someone with your information on your behalf and help set you up with someone to see locally. This is important for your long term health, Mocha. I really understand a mis-diagnosis eroding confidence in medical help (I went 25 years misdiagnosed with a health issue that, once known, was so obvious) so I know how hard it is to trust a new person to be helpful and effective.
But BB is so right about what a talented, bright, terrific person you are, and with some adult support, how well you will do in life over time. I am so sure of what you offer the world that I want you to get your network of support solidly in place in this new environment. Sometimes parents just don't see us clearly, and you need the solitary attention and devotion to your well being that a good therapist will provide. Just as your cat needs a good home with personal attention and people who will attend to her medical and life needs, you do too. So I hope this helps and am, along with BB, sending more [[[[[[[[[hugs}}}}}}}.

And btw, even if you rehome your kitty for her own good, you will have many opportunities later in life to have your own cat again. When it's your home and your decision. It's not a closed door, just a postponed lifestyle.

I have a great update!

So... I had a long talk with my mom a few days ago and after I settled down she talked me through things to see things that were not clear to me. I kind of blocked my mind off and wouldn't listen to her before. Cloud is a very scared and nervous cat. I think it was something that happened when she was a kitten (wont get into that right now. Nothing bad like abuse or anything :p ) She HATES strangers especially men! even at our old house when it was only us at home she would hide in the basement all day and only come out a little bit. When we have family gatherings for Christmas or Thanksgiving she has peed and pooped in out side of the box because she is to scared (this has happened more then once). When ever we build something she would pee. We normally cleaned it up and it was fine but then it started getting worse. When no one was even home she started peeing more than once in my sisters room (which is right across the hall from the litter box. That was right before we moved her to our new place. When they came up there was some dominance issues between some of our cats and when they all went in the camper together she peed ALL OVER the camper floor and ruined one of Clara (our other cats) favorite house! After that she said we might not be able to have her in the house when it was built but she gave her another chance and after she peed 3 times in our new house she said she couldn't come back inside. As you can see she has had problems peeing over the past 6 years and most of that I was to young to even remember. She may have peed more times out of the box at our old house that we didn't even discover. I completely understood why she wouldn't want a cat who peed in the house. But I still could not understand how she could kill her for it. So she said that we could keep her if she stayed outside! My mom is going to try and talk my dad into building her a little house in the corner of our garage for her to sleep in! She will still be able to play with her brother during the day and he may even sleep out there with her some nights! I just know that no one would take a cat from a shelter who is 6 and has a history of peeing outside of the box when they is a cute cuddly kitten they could have instead. She has also had some other health problems in the past and the vet has told us many times that she was going to die. Any ways. I am very excited to keep her and I know my dad will build her an awesome house (you should see the shed she is in now!). I know it isn't the same as being an indoor cat but I know that this is 100% better then having her put down!

That is excellent news Mocha and if she had a habit of staying in the basement she will probably be very happy in the shed. Sounds like your Mum has given it a lot of thought. Your cat may still have a medical issue but it sounds like a long standing one that is possibly genetic and most likely not treatable. So the solution your Mum has given definitely is the best.

Mocha, I am so relieved to hear you worked this out with your mother. It does sound like an elegant and compassionate solution, taking your mother's feelings into account as well. From the project we watched you make before on your video, I wouldn't be surprised if you take part in building the little house with your Dad.
It does help to get as much information here as possible so we can offer well-informed suggestions. Clearly, your honesty about what you were able to hear and take in explains the situation at first, your panic, and your reactions. It is probably the most important that you and your mom were able to talk calmly about it and work out a plan for the next step of the solution.
I still want to urge you to follow through with a call to your former dr. to get a local referral. I think you need to have that number handy and the knowledge at the back of your mind that there is someone local you can call in a crisis. It's kind of like insurance payments - once you get them you rarely get sick. You just feel well knowing it's there. I think your parent's are doing the best they can for you, and all of your lives are complicated. It may help them to know you have back up support available too.

Roberta: She has been to the vet several times and had tons of tests taken. I think my mom said that she had been tested for something in the past?