Sweetpe, unfortunately by not eating or drinking, nothing much can be done other than some IV fluids to keep her alive. She is going down because the body cannot continue fighting the cancer and chemo. At some point, the doctors will run out of options.
Have you considered having a professional sit down with your mother and have her state what her wishes are in this battle? When a person refuses to eat and drink, knowing it is prolonging the agony and causing not only imminent death, but unconscionable and gruesome suffering, it's important to understand her motives. Without a strong will to live and a desire to go all in at this stage, all the medical care in the world cannot change the outcome. Is it her desire to suffer like this?
This may sound cruel but it is reality at this point. Your mother's desires outweigh everyone, as painful as it may be for loved ones. We all deserve respect and dignity and to have our wishes honored. Please consider taking the steps to get your mother more involved in extending her life or accepting her decision. Even a healthy person can't continue living without food and water. The "rejuvenation" we see from IV fluids is often because the brain is dehydrated and the replenishment only lasts as long as it takes the body to need more.
I am truly sorry things have been so difficult.