I use hotspots fairly regularly but then the data comes out of my inclusive allowance, I’ve also got a 4g tablet for when travelling.
In the past I’ve used something similar to a Mi-Fi and my parents still do as they don’t want broadband and live in the middle of nowhere, for what they use it works great, but when my kids turn it on and connect the speed annoys them.
Some phones are easier than others to turn the hotspot on with, but looking at your post she may need a new phone as well.