I'd echo what the others have said above... the local cats would adore gravel - it would be their latest, newest, fabby litter tray !
Here's a suggestion instead - build up a few raised beds (say in brick and mortar, with a few gaps left in the mortar for weepholes), fill with the existing soil and plant up your mum's favourite plants in those. Hard landscape the rest of the garden (Tegula setts give an instant *old* look). Those raised beds could also contain a few of her favourite herbs or veg and be at just the right height in future years when she has a bit of trouble bending over.