I'm not in an identical situation but similar "vibes".
You need to protect your own mental health first.
Don't torture yourself with thoughts of "she might have changed" as this is very unlikely.
The only thing you are actually in charge of is your own boundaries.
So decide what you are willing to do assuming she has not changed (if she as changed which is highly unlikely you will find that out by how she behaves and can re-think your boundaries at that point)
It might be " I can walk the dog once a week on Monday/Saturday ( or whatever) and arrange a dog walker that you pay for on the other days.
I can take you to the appointment on Wednesday but not Friday (your boundary might be that you can take her to one appointment a week)
If you send me a shopping list I can arrange an online delivery for you.
Think about things you might do that are lower contact eg, could you have the dog at yours for a weekend?
These are just examples. It is entirely up to you. My advice would be to start by offering something pretty small and being clear that this is all you are offering offering. See how you feel
You can always increase what you do, if by some miracle she behaves very differently ( she won't though)
With your siblings, you could explain that you are low contact in order to protect your mental health. You can't just let things go as trauma isn't like that. It hangs around and you have to find ways to manage it. Your way is to be very low contact. They can't tell you how to manage it. Hold boundaries with them too.
If you are not used to it and have a family history of manipulation then holding a boundary without feeling guilty is hard. It may help to keep telling yourself " I am doing this to look after my mental health. It doesn't help anyone if I become ill and my mum ( and by the sound of it your siblings) can't/won't be mindful of your needs.
If you can afford it some counselling/ psychotherapy might be useful (some workplaces have schemes). You might also find it helpful reading about relational trauma and cptsd ( not the same as PTSD) and there are lots of articles online.
I think these podcasts are very good
https://insightpodcast.com/about-us/