OK, back on this.
I just took a look at my mums phone and a few observations.
1. She has used 127.6Gb or her 128Gb local phone data.
2. The iCloud section on the phone is greyed out. Apparently I am meant to press on this and this is where it will allow me to purchase more iCloud storage. Any ideas why its greyed out?
3. When I looked at the break down of what was using most of the data on the phone it looks like photos app, Facebook and WhatsApp are the major culprits. icloud is sitting at 5gb which I imagine is the default max you get for free.
So my question is how will purchasing more iCloud storage solve the issue with the local data storage on the phone being consumed by the main culprits being the photos app, Facebook and WhatsApp?
I find WhatsApp quite bad for cleaning up - even though they heavily compress images and video. It's surprising being in a few groups with people sending photos and videos of stuff how quickly it all adds up.
If you go into WhatsApp settings and manage storage, it'll show contacts/groups that have the most data stored - she'll need to be brutal in clearing them up.
It's a shame they don't have the ability to apply retention settings to contacts/groups - i.e. delete everything after 3 months.