Window eye line height is a very important factor when choosing a WAV, my family has had 5 vehicle over the years and we had to change from a VW transporter at the next lease to a Mercedes sprinter to get good vision for my eldest son.
Measure your mum’s eye line height while sitting in her chair to the floor , then make sure you ask every dealer/seller for the height of their vans windows, its an easy oversight yet a critical one .
You need a good 2-3 inches height above that eye to get good views out the side windows, also watch out for vehicles with big side pillars at the point your mum would be sitting, blocking the side view……home demonstration is an absolute priority…..good luck.