I've never heard of Sheila, no idea who she is lol.
I've heard of her, from Down Under.....

. Only kidding, but as NSEWonderer says, I also believe it was part of the back office systems involved in producing diagrams.
The 158/7 Driver duty posted above is (for me) an interesting comparison to many diagrams I was familiar with on my old patch.
I have no knowledge of the agreed walking times (platform to room etc) applicable to either Inverness or Aberdeen, but there appears to be approx a half hour of flexibility built in to that diagram around (or
after to be precise) the PNB, which if applied to my area would have been timed 14.17 to 14.57, so the return walk to the train (1A22) and associated PC/MOM gives a good degree of resilience, should the incoming train the driver was 'Passing' on (1H55), arrive late.
My point here being, is that this example represents good diagramming principles, in so far as contingency has been built in to the diagram, possibly purely as a result of the timetable itself, but none the less good planning.
My own experience in my last few years on the job, was that there was a tendency from some new (senior) kids on the block to require diagrams to be produced in a way that maximised productive driving (or guarding) based on computer generated minimum allowance information alone, so one was left with diagrams that were designed around the bare minimum legal requirements, which left no resilience in the plan.
I have no doubt the individuals concerned were themselves under pressure from further above (DfT etc) at the time, to maximise productive use of resources, but how far does that go before the service falls to bits on a day to day basis?
Feel free to ignore my old school grumpy methodology in these matters
