I figured out how to replace broken bits of the XML structure with identifying placeholders without actually opening the content.xml file, which enabled me to do the conversion, reconstitute the ODT file, and then open it in OpenOffice; then I was able to search for each of the placeholders and fix the problems manually. I've now done all of the tweaks listed in the posts below, but there remain some obvious issues with slashes and backslashes, which should be easy to find and fix. Then I can pass it back to PC for her own manual fixes.

One note to self: while I've replaced all triple-periods with ellipses as below, there appear to be no instances of the "ã…Ã" sequence in the document now, so I'm not sure what to conclude. I should advise PC to look at all instances of ellipses to check if they need angle brackets or not.