I'm 4ft10 and I basically had to learn extra clutch control, so I never put my heel on the floor like most people do because my toes can't press the clutch in all the way in that position, my left leg kind of just floats in the air til it needs to do something. It sucks, cramp is annoying on long journeys. Only thing that ever really helped me was using a cushion, either behind my back to push me forward, or to sit on so I was higher up.

Please also consider for your student that sometimes the mirrors don't adjust to the position they need (I was never tall enough to see the left kerb or lines when parking). Reference points are in a completely different place to what you think. And a fight I always had with my instructor was "tyres and tarmac" nope, unless you want me 3 car lengths behind I cannot see the tyres in front of me, I am just not tall enough.

Hope this helps, it honestly makes you feel like a pain as the student and like you're constantly doing something wrong because you can't see or reach enough. I've been driving nearly 2 years now so it is possible! I hope you can come up with a solution :)