A close friend has a 16gb iPhone 5 with no available storage. Where is all the storage used? Message history. I'm not kidding - zero non-default apps, very few

A close friend has a 16gb iPhone 5 with no available storage. Where is all the storage used? Message history. I'm not kidding - zero non-default apps, very few photos, message history for presumably the entire time she has had an iOS device which consumes (according to iTunes) over 14gb. The real kicker is Apple has provided no first-party way to extract images from message history. (EDIT: I am aware of the "keep entire message history"/"keep 1 year message history" setting - we are trying to extract photos from backup using 3rd party software so we can flip that switch. This is very non-intuitive and requires the use of an external device)