It sounds like the files aren't being fully downloaded, which would also point to a connection problem. We don't make any changes to your files and the same file is being delivered to every buyer so it can't be a problem with the original file itself or everyone would be having the same issue.
Normally what you have already done should have done the trick, since buyers who have problems with their connections during downloads can usually get the full file after trying again later.
If you are providing all of the parts of the bundle in a single ZIP file then it is likely that the buyer just isn't getting the full download completed, but has received enough to access some of the contents. Otherwise, if there are specific download links within the bundle the buyer should try downloading from them again, you can reactivate those or use Send Free Download Link to just send the links for the affected files.
Also, if the buyer has any third party "download accelerator" software I'd recommend that she disable it. Those programs can actually interfere with our download links rather than help things along, many programs of this nature try to access the download link multiple times to download several portions of a file at once, which may use up all of your available attempts and leave one or more portions incomplete.