Password recovery via email (or mobile phone?) is one option if they can get access to that. I don't suppose she's logged in anywhere, or has passwords saved in a browser? Even if there was something hacking-related you could do, it would be very illegal and would just make the situation worse.
It's not what you want in terms of adding the friends back, but Facebook does have a procedure for reporting deaths
. Maybe the family could contact them about the removed friends, although I doubt they'd do anything. Setting up a separate memorial page (possibly on Facebook) might be the best option.