Mom diagnosed Stage 4 NSCLC with mets to brain, adrenal glands, liver and renal

My mom was diagnosed on May 4th with stage 4 non small cell lung cancer, poorly differentiated, adenocarcinoma. She has at least 15 mets in her brain in all the lobes, mets in her liver, adrenal glands and renal.  The primary tumor in her lung is 9.6 cm at its largest and it is invading the chest wall. she also has a smaller secondary tumor, same lung.  Left lung is clear. Its in her lympathic system - on same side of body.  Clearly its travelled through the blood to get to her brain.

This was diagnosed because we went to ER because mom thought she had pneumonia that wouldn't go away and she had actually coughed out three ribs that we thought were pressing on a nerve ---which turns out that part was the brain tumors (she lost almost all use of her right side).

Mom is being treated palliatively with WBR (whole brain radiation) and finishes that next week. Then they will do radiation on her lung.  They want to do palliative care with chemo as well. We know this is a whole body disease.

What I don't know, is how long can you live like this?

The radiation has given her back most of the use of her right side, or maybe that was the steroids (4 days left on those).  She now has a slight stutter, sometimes worse than others, and sometimes struggles for words. She also has some short term memory loss and will just bounce between things she is talking about and is hard to follow.

She thinks she can survive for years, and I hope she can if its good quality of life, but I want to be realistic here as well...........