The ‘you aren’t working’ and ‘doing nothing all day, every day’ is infuriating isn’t it?
Care is so often seemingly invisible to others.
The amount you have been doing seems invisible to your sister and that is very hard.
Has the amount she has been doing been invisible to you though?
The cost in time, money & worry to go clean, bring washing back clean, dry and return, all the driving to apps etc
As a carer to your ASD, ADHD, developmentally delayed child you will know all the costs to you this places on you coping alone even though you love him dearly.
Perhaps a conversation clearing the air is possible and finding a way forward that honours both of your care, time and financial efforts?
I am always a little surprised on threads describing female parents being abusive where the (grand)children have diagnosis of some form of ND that it is never really suggested that the parent may have also been ND and struggled because it was not recognised.
It’s very nearly always mentioned if a woman is struggling with a ND child and the father is being difficult ‘he’s probably x as well’ to explain his behaviour.
Your mother may be an absolute horror with or without any ND, your sister may be minimising your caring duties for your DC and vastly overstepping telling you what to do.
It is also possible that your mum struggled in your childhood, that ‘being difficult’ was you struggling as a child, your sister as a young teen was not responsible for you.
Each of you three have been trying your best to cope and are doing your best to cope now in a society not set up to acknowledge the importance of care much less actually support carers.
Could you approach this current situation from that angle?
Have an open conversation with your sister?
Perhaps a way forward is possible whereby you can support each other.