[Quoth]

The publisher might have edited etc.
She might have used a PCW8256, Wordstar, Wordperfect, orphaned MS Works, orphaned Word for Dos, earlier orphaned Word for Windows, Wang, or even a typewriter.
Depends how long ago.
Novel might be on floppies (8", 5.25", 3.5", 3"), Zip drive or whatever.
OS might be CP/M, DOS, RiscOS, BBC Micro, Apple II, Xenix, Apple Mac OS 9 or earlier.

Authors are not IT experts and even to end of 1980s work might be typed for submission.

Some authors published even 60 years ago might be alive and republishing. Though wordprocessing "arrived" in early 1970s on dedicated systems it wasn't generally available till late 1970s Wordstar on CP/M. DOS based word processing wasn't affordable till late 1980s even though IBM PC came in 1981. That's why so many PCWs (dedicated WP with DMP, later cheap daisy wheel) with Locoscript sold. CP/M was included but a CP/M wordprocessor was extra.

Some published authors STILL write long hand and pay someone to type it up.

Or her version computer files might have got lost. I've lost two works in the last 45 years. One was a History of Communications written in 1986. It might still be on a 3" disc, but I think the disc got lost moving from abroad. The other was a ST-TOS fan-fic I wrote for my son in the early 1990s. There should have been a backup. There were multiple paper copies. But by 1998 it was missing. Fortunately neither of those is really important. And I was expert at IT & backups etc by 1983, using CP/M, DOS, UNIX, ISIS 2, OS/9 (not the Apple one) and VMS by then.