I do see both of them stretching the truth to make their point. If you draw a line from 1910 to the arrow on the number of people getting sick it did go down by about 50,000 cases per 100K over a course of 50 years.
Though their is a significant drop after vaccines.
Except there is one major concern for proper statistics.
The peak deaths (60 per 100,000 people) which suggest the highest number of people getting measles was in the 1880's before there was a measurement of people getting sick. They only charted deaths.
Isabella B. also used an extreme case in the Netherlands of a religious group that had a higher death rate then pre-vaccines then the peak in the 1880's. This is obvious deception.
That doesn't mean Isabella is wrong it means she is cherry picking to make her case sound better then what it is.
After reading these charts I do not see either Isabella B. or Dr Suzanne Humphries as quacks as you suggest.
They both simply have a different perspective of what is a rational course of action for these disease.
just a few links on Humphries.
And my personal fave... https://www.quackwatch.org/ is a treasure trove.