Well, that sucks big time, NoCo. Do you still have all of the original source? The slides and prints?
I've scanned and repaired slides and prints, some nearly a hundred years old, and I know what a hassle it is.
I am a fiend for backup, though. I have an always-connected external drive that is used for backup, and I also attach spare drives and clone the drives in the computer from time to time. It may be a bit of an overkill, but all of the time I spend on that is trivial to what it would take to reconstruct just one drive. Hard drives are so damn cheap today that no one should ever suffer from the lack of backup.
If you ever get things straightened out with Flickr, I would love to see some of your sister's work.