Hey, I just wanted to remark (again) how similar some of your mum's steps of progression are to mine. Like her, my voice is very weak, and although my speech is not normal, it is intelligible. As for FVC when I was first diagnosed, it was at 102%. 4 months later it was around what your mum just tested at. From there it was in the upper 70%, and they told me that even though the technical score was rated as "fair" that it was actually good. This was when I started using bipap.
My last test showed mid 60%. I kept insisting the lower score was due to leakage from lack of a tight grip with my lips, so the RT got me a full face mask to try, but my score did not improve. Nowadays, I do notice a difference when walking, or laying flat and so forth. This STUPID cough that I have is different too, I run out of breath coughing, I have the reflex, feel the need, but can't get the air out. The last couple of nights it's woken me because of this, then I lay awake pondering it LOL.
I do have a question/suggestion about her not walking much. Does she use her cane for strength or balance? I ask because I've found having AFOs gives me so much more freedom and independence. If her problem with walking is greatly influenced by a compromised balance, then the AFOs would not probably be enough.... also, interests to keep her "going"... this puppy gives me lots of reasons to walk outside, and I've really enjoyed the autumn leaves. Its my favorite time of year anyway, but, having to go out rain or shine has been good for my soul, so to speak. In all honesty, a puppy was not the wisest choice, a grown (read: calm) dog would be better for a PALS unless they have a lot of support from others willing to get up during the night, etc.
Your mum is so lucky to have the patient and involved daughter that you are!