Hi, and i`m sorry to read about your mum`s condition.
My late husband had colon cancerso I know what you`re going through.
The constant bowel motions could be either of two things:
1. Simple loss of control due to the tumour causing frequent bowel spasms. What helped my husband in this case was taking codeine phosphate (to slow down the bowel contractions) prescribed by his doctor.
2. Alternatively, it`s possible she is constipated/partially obstructed whereby the loose frequent motions are the fluid part of the stool bypassing the obstruction. Hence its difficult to treat without knowing the cause as in this case the opposite treatment ie fybogel or similar to cause a proper bowel action would be in order. Your mother`s doctor should examine her and decide which it is.
The substance she is passing will mainly be the fluid released by the bowel walls in response to the tumour/constipation or obstruction. This can make her dehydrated so you need to keep her drinking little & often if you can. Hope you get the medical and psychological support you need through this difficult time. Best wishes, and hope this helps a little.