Many thanks for all the replies. The current plan is now:
- transfer photos and videos from GoPro to iphone using the lightening to USB 3 camera adapter.
- where she has internet, this will upload files to icloud (with a 200GB icloud plan and photos optimised switched on)
- also transfer files to WD mypassport wireless as a 'local' backup for when no internet.
- delete files off SD card when files have uploaded to icloud.
A bit expensive relative to some of the other options, but she flies out in a week and there's no time to get stuff from overseas.
Not completely failsafe - but best in the circumstances??