Im perfectly content knowing just vague information about individual ancestors 3-4 levels up, and basically nothing on level 5, except the odd church record of births, marriages and deaths giving a rough indication of where some of them lived.
The people 5 generations back deserve much less thought space than the community you cultivate around yourself today (including living family).
Sure it's kinda cool to see some fragments here and there. But would I want it to be the standard that we keep all the emails, chat messages, phone camera roll, GPS logs etc of people... Hell no. I'm not advocating for absolutely forgetting everything. But we have to filter.
If you want to be remembered, live a life worth remembering.
It would cost around $3000 to have the diaries scanned today, this number was way higher a few years ago (which my mother didn't have). I know Americans have a lot more storage space in their houses and use storage facilities for a lot of things but there has to be a cutoff point. I have about 6m3 of (already filled) extra storage space in central Stockholm and wouldn't want that much more. Throwing shit away is a part of life.
A few years ago , There are auto sheet scanners that scan both sides of pages relatively quickly , like 1 or 2 seconds a sheet, and can do at least 50 pages at once.
And I'm sorry your mom experienced that weight towards the end of her life. That sounds like a significant thing to grapple with, especially considering some of the not so pleasant content mentioned.