Hi Sal
First of all, I am so sorry to hear of your news. My mum passed away from breast cancer after a 3 month prognosis in August last year. One of the most devastating things is that our family wasn't the first and won't be the last to feel such pain, so my thoughts are with you and your family.
I understand your desire to know what happens next. My mum and I were both very much like that too - very organised. I recall mum often saying, "they said three months, its been one and a half and I'm still walking! what is this all about!" I guess it happens differently for everyone, and depends on a lot of factors - what meds your mum is on, and whether she is staying at home or going to a hospice.
My first recommendation would be to talk to your palliative care nurse - our family always respected them for their honesty, and they really do know what they are talking about.
How much do you want to know in terms of physical change? It can be a lot to take in at once, but I found knowing what to expect helped me. I just don't want to frighten you.
Like your mum, my mum slept and rested a lot. This is often a side effect of meds, but my mum said she was "readying herself" or "packing her bags". It frightened me a lot when some days mum would only wake up for a bit in the morning or the afternoon. As the cancer progressed, mum was more and more tired. Towards the end, it was a blessing to have a conversation with her, or for mum to stay awake while I showered her. This is okay, you need to let her rest, and don't push her - your mum doesn't need anymore pain than she already has.
In terms of pain levels, it does get worse, and as an onlooker its devastating. The fact is, things get worse. Have faith that there are tremendous amounts of medication out there to help. The palliative care nurse can help you with this - and really make sure your mum makes use of it. Sometimes my mum would be a trooper and say it didn't hurt as much as we knew it did - but again, the help is there.
I guess the third thing that was a huge change for me and I can't really come to grips with still to this point, is the side effects of the really strong pain killers. One being the sleepiness which I mentioned earlier, but the other being kind of high. Mum started talking about funny stuff that didn't quite make sense, like dreamland. She told my 15 year old brother to "go to the girlfriend bank". You've got to giggle at that stuff with her, but its also heartbreaking because thats not something my mum would say. Its like she got delirious with the meds. This happened towards the end, and made me feel like id lost my mum before she physically went.
The only advice I can offer you, is to not rush things. Don't feel like all of a sudden you have to be sad or be with your mum or that you need to squeeze everything in. Enjoy each others company - ask about weddings, pregnancy or girl stuff. Chat, drink cups of tea, and soak up what you need to from your mum.
My mum and I had a bit of a tradition - drinking baileys on ice in the afternoon with a tiny snack (what you said about appetite is spot on). But try to make the most of the little things, as pleasures come hard to find when you're restrained to your bed, but you can make it a happy time too.
Best of luck, I'm so sorry that this has to happen to your family. Be strong for your mum, and look after yourself. If you need anything I'm here.
Emma xx