Another one here to say that, darling, you are not an idiot. You've been through hell, going through a terrible time and are ill. Anyone would struggle with the basics in your shoes.
I had to build up self-care again after a terrible time with depression and I focused on the smallest things, and just doing one small thing at a time until it felt like I'd established a habit. I focused on how it made me feel good, so that I was incentivised to do it the next day and the next...
Remember that habits take time to build and you'll fall off the wagon a few times. That's OK, that's normal. Just start again. The gaps when you let good habits drop will get shorter each time and each time it will be easier to pick them back up.
Blood tests are a good place to start. B12, iron, vitamin C, vitamin d...Vitamin C deficiency responds surpringsly quickly and these are all things which promote hair growth.
Don't let perfect be the enemy of good. A quick once over is better than nothing, even just a rinse with mouthwash. Whenever you achieve even that, you train your brain into a new self-care habit which you can grow.
Aim for 1 nutritious meal a day.
Can be super-simple, like omelette or tinned fish and jacket potato.
Ready meals are fine but try and choose less processed ones (Charlie bigham is good, you want foods with an ingredients list you'll find in your cupboard)
If you eat terribly one day, that's fine, try and make sure you have a piece of fruit the next day.
Baby steps, little wins.
Write down your little wins each time so you can see how far you've come in a few months time and which ones you might be ready to build on.
Consider every day "how am I nourishing myself today? How am I taking care of myself?" If that means you need to hide under the duvet, that's fine.
And remember, darling. Many people with a history of SA and trauma carry feelings of not being worthy. And you are, so so worthy of self care, compassion and love.
You'll get there. Don't beat yourself up. No insults, OK?