How can I simplify managing an Excel-based static webshop?

Why not just share a link to an Excel file on Office.com without edit privileges? That way, she can still interact with it without mismanaging the essential data.

Consider locking the specific cells in the Excel file she shouldn’t touch. You could also put the file in Google Drive and link to it on her site, or even embed it—though I'm not sure how that would work. This way, she has control over the manageable parts, and you can handle the uploading.

Instead of trying to fix her Excel mess, just build your solution around it! Keep her sheet as the source, but use a script to clean it and convert it to JSON for your site build. This keeps things simple from her end while structuring the data for your site.

Bring back MS Access! You can set up an Excel sheet that's locked down for her to play with, but add layers of validation and structure that she can't alter. Have a clean version of the sheet that she can’t access, and implement a system where she can validate her data and prepare it for upload while you control the uploads to your site.

You might want to invest some time into enhancing the validation of the CSV in your current setup. Think about using a static site generator to create individual HTML pages for each product row, which could help organize things better.