A reddish tint to his coat could be caused by being near time to moult, being caged in a way that he can contact urine (caged next to another male?) or from just lying in the sun. It's probably not caused by the digestive issue.
Unless....he has wool block from swallowing too much moulted hair? Either way, if he's not eating, measures to prevent gi stasis should begin ASAP. It doesn't matter what the cause, if his digestive tract stops...he's a gonner.
A dehydrated rabbit can appear to become extremely thin in a rapid amount of time. The spine will become very easy to feel almost overnight.
She should observe his stool. Is it diahrea, or is it smaller than normal stool? Has he stopped passing stool?
I suggest unflavored pedialyte along with the mashed pumpkin. Also old fashioned oatmeal and good hay to replace pellets for a while. It's been my experience that rabbits will often eat greens when they refuse other foods, so she might consider offering some very mild ones like parsley or cilantro. Grocery store fennel has also gone a long way towards getting rabbits to eat willingly for me.
If she can find and ID wild plants, offering fresh rabbit safe greens is a good way to keep the bowels moving without force feeding. Although, if he's been refusing to eat and drink to the point of dehydration, she will likely have to force feed.
