It's possible your mum is hovering her finger over the screen too close and this is causing enough of a response (it works via electrical charge) to make it "feel" super sensitive. Synaptics are the company behind 99% of digitisers (thing that recognises your finger) used today and while they expose a lot of controls to phone manufacturers (eg centre point calculation, amount of touching stuff to recognise as touch, how to recognise palms etc...) most phone manufacturers use the same level of response so people can all use phones in the same way.