How to get fluids for dying mom when the hospital won't take her and hospice doesn't give them?

You can’t be providing fluids to a patient whose kidneys can’t filet the filter, you could then cause fluid retention leading to possibly CHF. The Catholic Church shouldn’t even be making rules like that, they aren’t physicians. Your mother is in the process of dying, let her pass in peace, not eating and drinking is a sign of this. I know this from experience, my mother did the same thing.

Given that this post is now 1 month old, I have to assume that the OP's beloved mother has passed. I hope that her death was peaceful. Bless her soul.
I worked as a Hospice RN for many years and among the most difficult things for families to let go of at the end of life is the provisions of food and fluids. Sharing meals is so much a part our family life, evoking memories of all that is central to families and this is often a large part of the end of life teaching and care that is done by Hospice nurses: helping families to let go and accept the dying process.
Once a person begins to cease food and fluid intake, pain is lessened as part of this natural process and allows for the brain to produce endorphins that aid in alleviating pain. The provision of IV fluids is a life-prolonging measure that is contrary to the body's natural shutting down. Major organ systems fail and eventually, loved ones' hearts cease and they breathe their last breath.
Hospice care was the last of the areas that I worked in as an RN and I carry memories to this day of such poignant beauty that it takes my breath away to see, in my mind's eye, the images that I'll forever carry of loved ones in their final hours. It was a true privilege and honor to have been a part of the last moments of the lives of my Hospice clients, all of whom passed in their homes surrounded by family, as many as 4 generations of family.
The Hospice that I worked for was part of a Catholic-affiliated hospital and most assuredly, the withholding of sustenance is not considered as anything other than allowing death to progress naturally when every measurable indicator says that death is coming. I find it unimaginable that any tenet or belief system would promote any measures to prolong a life that is ending or promote interventions that would only serve to prolong the dying process.
I hope and trust that the family of the OP were gently guided in the loss of their beloved 97 year old mother and now hold precious memories of those final days and hours.