SharePoint user adds random metadata to files

One thing to check is metadata already stored inside her files, especially if she creates them from an old document or template. SharePoint can read matching Office document properties into library columns, even when no column defaults are configured.

Try uploading the same affected file through another user, using a different filename to avoid overwriting anything. Also have her upload a completely new document that wasn’t based on an existing file.

If the unwanted values follow the file, open it in desktop Office and check File > Info > Properties > Advanced Properties, particularly the Custom tab. Correct the relevant properties in a test copy and check the original template too.

If the values appear only when she uploads—even with a fresh document—check Power Automate flows or other library automation for conditions tied to her account. Version history may help show whether the metadata arrives with the upload or is changed afterward.