My mother has a bad hearing problem and wears 2 hearing aids. She tells me the air pressure is worse for her in the back of the plane than the front. I would like to know if this is true - is there a difference in air pressure depending on where you sit in the plane?
As stated in other answers, in steady flight there is no pressure difference along the length of the cabin, and only a miniscule one during lognitudinal acceleration.
What your mother might be experinecing is actually low frequency sound/vibration that can sometimes feel like fluctuations in pressure, a sort of a bubbly feeling in the ears.
This will vary greatly on type of aircraft, seating position, stage of flight etc, but as such it is not at all implausible that in general your mother experiences this in the rear portion of the cabin more than in the front. This can be especially prominent in planes with wing mounted jet engines, since the exhaust nozzle will be in front of the passengers sitting in the aft section.
There may be other factors than a pressure differential as the cause of ear irritation, such as greater pitching accelerations, because the rear of the plane is farther from the center of gravity. This could cause general motion sickness, and for some one with issues with their ears, in particular, the vestibular system$^1$, an increase in feelings of vertigo.
$^1$ see Pathologies
The difference in air pressure between front and back of the cabin will be trivial to the differences felt in pressurisation between the aircraft climbing and descending; or adjustments made to the ventilation controls.
Discomfort is far more likely to be due to the sound and vibration which will have a complex distribution depending on the type and layout of the aircraft and the extra motion typically felt in the rear seats being noticeably more bouncy, and during acceleration and deceleration phases.
You might find the centre of the aircraft is the best position rather than the front, and definitely not the rear.