Answer: a nettop will be a reasonably best option.
Explanation:
What is a nettop?
A nettop is a smal size , cost effective and a computer which uses less power.
It has simple use ,one can use it for browsing the net, listening to music and accessing any internet based services without fully using the computer for other complicated services such as typing essays or anything extensive .
It is just for basic simple use of computer.
This will be effective for a 72 year old Helen who isn't looking to do anything intense on the internet but who just wants to communicate only.