Hi

I'm sorry to hear of your MIL's diagnosis. My Mum had peritoneal cancer ovarian origin and her illness also caused bowel blockage and vomiting. When she was advised that her condition was terminal and that chemotherapy was no longer effective she survived just a further 8 weeks which was spent initially at home then at the local hospice where she passed away. The illness initially waxed and waned with regards to being able to pass stools and having better days, mainly because the medications, including steroids, controlled some of the inflammatory process and supressed the nausea and pain. 

We were advised by the palliative care team that if you can see deterioration in terms of weeks then that usually is an indicator that the patient has weeks left, if in days then days left and similarly with hours. Take things a day at a time, if she has good fortune to have a day of energy and positivity then make use of it and be prepared that some days she may not have the same capabilities. 

I wish you strength as a family to cope with the future and treasure the time you have with your MIL.