Yes, there is a way to do it on one go.
In the Inbox you will find the multiple notifications of changes to events. Long press on the first OK and you should get an option to OK all the notifications.
If you'd enquired here before she embarked on this project the advice for another option would have been just to go into iPhone settings and choose to present (to sync) on your iPhone calendar just the most recent events (there is a selection of numbers of months) rather than have all events from the past visible. I'm not sure there is anything to be gained by deleting old events, and I have found it useful to see what I was doing on a particular day in the past.
EDIT - I just saw that while you have an iPhone listed you were asking about a Mac. Let me look at that too!