Firstly Clipped I'm sorry you're going through this, it's utterly utterly shit and my thoughts are with you and your family (as much as the internet allows) x
You've had some fantastic advice here, and good explanations and all I can add is that if nothing else, you have to remember that it's a PATHWAY not an instant denial of everything.
My neighbour died at home, so once he couldn't sip water (with help) he couldn't get water at all and this did (in my limited opinion) hasten the end, or rather, did not prolong his suffering. (we, his random neighbours and son, did moisten his lips with water when they 'looked' dry, but that was more to lessen our distress at him looking uncomfortable - nothing wrong with that either).
I do feel the LCP is misunderstood, and that the very very few cases where it has been mismanaged have cast a shadow over what is probably the most humane end of life care we've ever known in this country. It is compassionate, and designed to lessen distress near the end, not increase it.
I wis the 'pathway' had been more utilised when my MIL needed it, with the best intentions of family and no clear plan, she suffered needlessly.
I sincerely hope the end is peaceful for your mum, she's sounds fab, you need to believe you are a good daughter too and it is always alright to question things, because you care. x