You are very young to be assuming the burden you have undertaken. Even when we are older it is overwhelming to face a parent's illness and feel helpless. Is there anyone else in the family or a friend who you can talk to? As difficult as it may be, you must realize that your mother is entitled to a say. Ask her if you have her permission to consult with other facilities.
Please remember that doctors were given permission to heal, not to predict. Don't be so afraid of the "6 months." Read some of the stories here and you will see that doctors are neither mathematicians nor prophets.
You are at a very fine facility. Speak with the doctors involved in your mother's treatment and ask them if they have any suggestions beyond the care she is now receiving. It is never an insult to a doctor to request a consult. The doctors at such a facility have a better knowledge of who may offer the best input on your mother's care than can any lay person. Also if you do decide on a consult, exact information on your mother's history including all treatments, tests,etc. can be transfered properly, easily and precisely between the facilities. There should be some omsbudsman, case worker or some such who can help you with this.
May the One whose commandment to honor your mother you are so lovingly fulfilling give you the strenght to go forward with whatever you decide.