Firstly, it is a medical decision as to whether there is any chance of success.
Given what you have posted about your mum's health - dementia, ulcer eroding into an aortic aneurysm amongst other problems, and her age, if her her heart stopped beating and she died, the chances that she could be successfully resuscitated are remote in the extreme.
The chances that she could be successfully resuscitated to the same quality of life that she has now are even more remote.
If she has capacity, and that is not clear either, any decision about wanting to be for CPR is hers to bring up with her doctors. She would need to discuss this with her GP, now she is at home and see if they felt medically there was a chance that she would survive CPR. If they feel there is not, which is overwhelmingly likely what they will think, she would be entitled to a second opinion but be prepared that the second opinion may think the same.
If she doesn't have capacity, you can ask for the same reviews in her best interests but ultimately it may end in the same results.
What comes over to me is that you are not happy with her care, both her personal care and her medical care and would benefit from a sit down discussing having the realistic goals of her medical care explained to you and coming up with a mutually agreed plan.