The most basic function is the control of heart beats and spontaneous breathing. Other more complex functions may include control of eye movements and some of the sensation and movements of the head and neck. Given the injury she has suffered, she most likely will never be able to respond to her environment in a meaningful manner. This function level may range from what is known as persistent vegetative state to coma. It is difficult to accurately predict what life expectancy is in these cases.
Some patients survive for months to years.
I am sure that this has been very hard for you. You may wish to discuss her situation with her doctors as they are more aware of all the details of her care. I hope this information will help you. Information contained within this forum is intended solely for general educational purposes and is not intended nor implied to be a substitute for professional medical advice relative to your specific medical condition or question. Only your physician can provide specific diagnoses and therapies.