If she is severely impacted though water and roughage is not going to be beneficial. And if there is a strangulation or other blockage then adding more food, including roughage, is going to be like putting more hair down an already plugged drain.
The doctors can manually unimpact her for starters to allow some movement. They could also possibly do a ultrasound or MRI to rule out any masses that could be causing a blockage.
And you are right, the mother needs to get on board. As much as I hate doctors and think the vast majority of them are ignorant quacks there are times when they are needed as well as some of the diagnostic equipment they have access to. This is one of those times.