It wasn't perfect — but 7z has built-in error recovery for split archives. If she padded a dummy 004 file with zeros and used 7z rn (rename) to renumber the parts, the archive might still extract, skipping the corrupted block.
She created shadowoftheerdtree.7z.004 as a 50 MB dummy file of zeros. shadowoftheerdtree.7z.004
Then she opened a terminal and typed: