An oxygen concentrator and a ventilator running 24/7, alongside the other things mentioned such a humidifier and suction machines. I can certainly see how that would add up quickly. Let's say all the equipment together consumes 600W, which is probably very conservative. At a price of 24.67p/kWh (which is the average price, so she could very well be paying more) that's £3.55 a day on top of regular household energy use.