I have a few additional questions please.
1. When did that hair loss first start?
2. What do you use on Sabrina for flea control? When did you last apply it?
3. Has anything changed in the household? Any thing that would cause stress?
4. Have you seen her licking or biting back there?
the hair loss started quite a while back, and then went away. a couple months ago my mother went in the hospital for a few months (she's been back for a couple months now) and i noticed the hair loss got worse then. she's an indoor cat, and we have a couple of cats that are all indoor so we haven't had a problem with fleas. she does lick a lot around her back and tail.
one detail i will add is that she is always hungry. she wants people food all the time (we don't give it to her but on rare occasions) but she stresses out about it ridiculously. she will camp herself out in the kitchen and meow insanely just wanting it badly. she's a very loving cat still, but i worry that stress could do that to her fur.
Now of course it would be important to rule out the other things like food allergies, environmental allergies, and food allergies. But it really is sounding anxiety related to me. Cats can have anxiety, and obsessive type behaviors, just like people.
You can try the aromatherapy plug ins, or sprays, called "feliway." You can purchase these at any pet store or online. It will help calm her a little but I feel like that will not be enough.
I think she will need prescription anti anxiety medication. It can be prescribed in oral forms or even in a transdermal form that absorbs through the skin if she is hard to pill.
I also want to mention that a ravenous appetite can indicate hyperthyroidism which is an overactive thyroid gland and therefore too much thyroid hormone in the body. A blood test can rule this out or in. It can be treated with oral medication. It is important to treat it as it causes high blood pressure which is hard on the kidneys and heart.
www.VeterinaryPartner.com/Content.plx?P=A&A=516 more on hyperthyroidism
www.VeterinaryPartner.com/Content.plx?P=A&A=2565 more on cats pulling hair out