It depends how well those ranked in the 80’s perform in the HSC. If your internal mark is 30 and external mark is 100. You get an average of 65 which is band 3. However if your peers in the 80s range improve and everyone in that rank of 80 get their average mark up to 50% for example you included, your estimated internal mark could be 50 and external would be 100. Averaging 75 which is band 4. Jimmy can double check if what I’m saying is total garbage lol.
There is also the possibility that sammantha's Assessment Mark may end up being slightly better than expected, the likelihood of which is dependent on the moderation process/her peers' performance in their HSC exam (as you mentioned), although this is a factor beyond her control.
Getting ready for the copy/paste season