I am so sorry to hear about your Mum.  I worked for many years in a residential home for the elderly and a similar situation arose there with two of our ladies. Their families felt very like you do. In both instances the ladies were prescribed Tamoxifen as their only treatment and believe it or not, one lady lived for a further 3yrs and the other for several more years than that - I am not even sure if their deaths were attributable to the cancer.

 I do hope your Mum's GP or consultant is someone you can share your concerns with and you can find a suitable solution to keep her as comfortable as possible. Remember to take care of yourself too x