My Mother Has Pulmonary Hypertension. We Spent A Day At

My mother has Pulmonary Hypertension. We spent a day at the ER recently due to some symptom flair ups. Her O2 dropped to 75(puse ox) . She is on oxygen 3.75 liters when resting, The ER did not find a "cardiac" event happening. My family has been asking me what all of the information means.
Is there a possibility she will improve or is this the beginning of the end? She is very fatigued and does no exercise and moves just a little (around the house). She has the sleep apnia type and I would say she is a functional class IV. She was diagnosed about 9 years ago. I just kinda need a time frame if possible to share with my family that lives out of state. If she takes her O2 off her O2 levels drop almost immediately to 84. I am sure there are many many things that contribute to someones death. I am only trying to figure out if PH is like CHF where at the end, it's a roller coaster ride of good days and bad OR if this will just continue to make her decline. Thank you