Hi Dani,
Nutrition is the only way the body can heal. If your mother is still losing weight, there is a reason why she doesn't look healthy. I know with all the pain it sounds like it would be difficult to eat but without nutrition, the body will feed off of itself. This is not good. With the pain wearing her down all day, she will not eat and without eating, she will not heal. She is in a loop and somehow something needs to be done to break the cycle. There is no pain worse than deep bone pain. It sounds like the doctors are doing something to address the pain. It might help if you steer your mother towards measuring her pain a few times during the day. It's the old from a scale of 1 to 10 how would you rate the pain. Maybe something will stick out as far as a time of day or something. At a minimum it will give you data to go back to her doctors and say look, her pain is always an 8 to 10 and this needs to be managed much better to give her some quality of life.
The coughing when eating or drinking, unfortunately, could be another "new" life event. I still cough and it has been almost 10 months since the end or radiation and chemo.
I don't think your mother will ever tell you how bad it really is but maybe you should let her know that it is okay to feel crummy with all she has been through. Get her to process some of the depression and help her see the sunny side of life. She has a lot to be thankful for, including having you by her side!
I am sorry she is having to go through all this pain and the lingering issues of this horrible disease. Get her body healthier and good things will start to happen.
Ed