Hi stella,

Sorry to hear about your mom's difficulties with here digestive system.  It's great that she's open to a long fast as this is an amazingly effective way of allowing her body to heal this particular ailment along with providing so many other unspeakable benefits.

As to your mom's weight and given her starting point, i would expect her to lose on average about 1/3 pound of fat per day which would be about 10 pounds in 30 days and 13 pounds in 40.   She might lose 30-35 pounds overall, but so much of the weight we lose in a fast is temporary, primarily water and secondarily intestinal content. If your mom fasted for 40 days i would expect her to get down to 100 or 105 at the very end of the fast then be back up to about 120-125 within 3 weeks of moderate and healthful re-feeding before leveling off. 

The number i would be concerning myself with is not the artificial low point, but the point my body will naturally return to after 3 weeks of eating. So in my opinion, while 40 days in your mom's case might be too long for other reasons (see next paragraph), weight loss is not one of them. 

It is best to take a long fast a day at a time and in many cases 40 days would be too much.  In my own examples, i broke my first long fast at 30 days after reaching genuine hunger at 29 days, 16 hours.  This was absolutely mandatory.  I broke the next one at 30 days for various reasons one of them being fighting with feelings of hunger (though not "genuine" hunger) from about 24.5 days to this nice round number of days... and the final one i broke at 36.5 days because over previous days i was enduring nausia and extreme exreme weakness and reached a point of feeling ok and viewed this as my best opportunity to escape the fast at a good time.  In this case i felt i could have entered into something dangerous had i continued and pursuing 40 days would not have been worth the risk.