As you mum is shortish think along these lines...
Avoid three-quarter length trousers because they make legs look shorter. Trousers should be full length, falling to the bottom of the heel
Don't wear trousers with turn-ups or wide legs, instead opt for narrow, straight legs or bootcut trousers
Skirts and trousers with high waistbands make legs look longer too.
Create the illusion of height by wearing a top and bottom of the same colour, drawing the eye up and down.
Longer length jackets worn undone also give the illusion of height.
Avoid chunky, ribbed tops that widen rather than lengthen the body.
Wear heels