Sorry you are unable to see anything from the link. If it's any help, the shortcut runs from the end of Shield Terrace, across the field towards Barwood Gate. There's not really any rough ground in the area, some of the fields look a little overgrown, but the aerial photos are about 5 year old reckon.
There is a sort of path through the field, but in the dark, it would be easy to not stay on it, which is most likely what happened to this lady. The reason people take that shortcut through the fields is that it's about a mile round if you go via the roads. It's not obvious from the aerial photos, but you have to go out of the town via Titchfield Street, and then walk down the A71.
It's well known that a large area of land around Galston has been mined, But the problem is these mins date from about 1830 until roughly 1900. The last known mine in the area closed in 1931, but most of the mining went on in the 1800's. These were coal mines, but are all long since gone.
Of course some shafts were recorded on maps, which survive to this day, but many are not. If there were any maps made at the time, they have long since been lost and so. There are quite a few sites in the area that have subsided or collapsed, but without anyone being affected. This lady must have been extremely unlucky. The collapse must either have happened while she was on top of it, or happened that day, or earlier that day, and she subsequently walked into it. I imagine it would be completely invisible on a dark night in the middle of a field.