Really worried about my balding cat

[ThisMustBeMyDream]

My cat is 10. I've had her for 2 years. She was a rescue with no real history.
She is quite a stressed cat - doesn't really like people until she is hungry. She sometimes asks for strokes but then bites and scratches with no warning (I'm scarred from her many attacks).
Now she is balding from her back half mostly. I first noticed it maybe 2.5 weeks ago. It has been quite rapid.
She is well. Eating as much a usual (she likes a LOT of food!). She isn't scratching at all. The fur she is losing isn't being dropped around the house or anything (she doesn't usually moult much and there isn't any extra noticeable hair about the place). She is up to date with flea and worming treatments prescribed by the vet.
I'm at a loss as to why this has happened so have made a vet appt. It isn't until next Monday however. Can anyone offer any advice in the meanwhile?

We do have a 9 month old kitten also by the way - both cats female. They don't get on particualry but will live along side each other. Have had the kitten since last June so not a new introduction or anything.... so I can't see that she is stressed over the other cat particulalry. Her behaviour didn't alter when the other cat came along.

Ive added some pictures. Balding is to both rear quarters, back legs and a patch on her side. The first pic is 8 days ago. Other two pics are from today.

Looks like a really typical flea allergy - are you certain the treatment you use is still effective?

It's advantage from the vet. I can't get anywhere near to check for fleas but we have had them in the past so I know when we have them (flea dirt is non existant plus the kitten has none, and as she doesn't go out she can only have them if they are in the house. No flea dirt on her either).

House is treated with Indorex.

Doesn't look like a flea allergy to me. Much more likely to be psychogenic alopeca given her history. It's caused by stress. I'd be using a feliway diffuser if she's generally stressy anyway. It often coincides with changes to their environment, new people/furniture, any sort of distruption. Even a new cat in the neighbourhood hanging around your property could cause it. Your vet might be able to prescribe anti anxiety meds.

When I first got her the first thing I did was get a feliway diffuser. It made zero difference to her behaviours. I kept it going for 3 months but it just had no effect.
I have some pet remedy which I tried about 3 months ago, again, no noticable differences.

Looks like classic over grooming due to stress. Wouldnt hurt to have thyroid investigated if she has behavioural changes aswell but likely that the kitten really upsets her. Cats are not great at putting up with other cats if they do not have a sociable nature. As mentioned the vet may prescribe something but that does not remove the problem. Ensure the cats do not have to share resources, they should have access to more than one litter tray, food and water bowls etc and make sure she has somewhere to retreat to where the kitten can not go. That might be enough to reduce the turmoil that causes her to overgroom or reduce the need at least. Hope thats helpful.

I was also going to suggest over grooming- my old cat did this and also had really sore skin underneath. It was really difficult to get her to stop, I used to put my hand where she was licking so she licked me instead but that obviously isn't a long term plan. Also used Feliway which helped her a little. I'd definitely see the vet. I hope you get it sorted

My cat did this. Vet said it was stress but she was such a chilled out cat. She then lost a lot of weight and it turned out she had hyperthyroidism. Like yours she was eating loads and she was same age as yours. Ask the vet for tests!

Given where it is I'd also agree it's most likely overgrooming. Get her checked out for medical causes but if that's clear, it's most likely a) stress (could be she's just discovered this new coping mechanism!) or b) an allergy to something. Even if she's up to date with flea treatment, one bite can trigger a reaction. A steroid injection could stop the itch from an allergic reaction so you could try that and see if it starts to grow back? Though if her skin isn't damaged at all you could just wait and see how it goes.

My cat looks a patchy mess most of the time, but I leave her to it unless she gets sore skin, then a jab normally stops her licking for a few weeks. She's obviously allergic to something but not figured out what yet. But mine has always done it, yours is hopefully just a one off thing.