My Mom Is A 98 Yr. Old With Her Mind

My mom is a 98 yr. old with her mind in tact. She has severe aortic stenosis and is now in hospital due to pulmonary edema. Her right lung is filled with fluid . She is on a bipap machine and receiving IV fluids and antibiotic, immopatin. She is asking to eat under the mask and has failed swallowing test. How long can she live on just normal saline? We are very confused about her care. Are we keeping her alive to no avail?