Sorry to send you another link but this might be of use as it discusses the final days of dying with cancer.

I have helped care for a few people who have died from cancer.  Mostly it was a peaaceful decline (thank goodness - for their sake as well as their loved ones) but sometimes I was surprised by how somebody could perk up suddenly for a short period.  When they are pain-free and at peace with the situation this can happen.  My son's father (we were no longer together) perked up at a time when everyone felt the end was coming close - sadly it did not last for a long period and he died within a couple of days.  The same occured with my next door neighbour who when near death could become aware of everything around him for short periods.  I don't pretend to know why this happens but it was nice.  I would sit and chat with  him about anything and everything and he was quite lucid in these periods.  I - like others here - have no medical training and cannot start to guess for how long this will last but, well, make the most of these waking periods to chat with your mum about whatever she wants.  I am so sorry you are losing your mum but you sound to be doing a good job.  Annie

www.cancerresearchuk.org/.../dying-with-cancer