I am so very sorry to hear of Fiona's current situation. It's not good news, the ascities. I am surrounding you both with positive energy now as I type this.
To answer your question honestly, and I think you need an honest answer, ascities is intracellular fluid that in almost cases with cancer builds up repeatedly, despite efforts to remove it via ports and drains. It becomes a terrible way to live and, at least for my Mother (who was 61), was quickly too much for her system to handle.
It may have been the series of events in her life previous to that occurring, but her energy waned quickly. She was strong, knocked down, and gone before my mind could cope with the thought of loosing her. I am so sorry not to offer you hopeful news, but you must prepare, and by your mere question, intuitively, you know this.
I hated to even consider the word hospice, but they helped support my Mom and our family through this difficult time. The people we encountered offered suggestions at every turn and they were able to give is reality checks as we needed them. Make her comfortable in any way you can.
(((Hugs))) to you both. You are right... this disease is horrible. Be brave and find support for yourself and Fiona quickly. -ljg