Hi @KIMBERLYREA - We normally will turn the Excel file into a PDF to upload it to the proofing tool. It definitely requires taking a minute to get the settings right to make it readable in a PDF, screenshot example below.
It would also depend how complex of a file it is...another suggestion would be hosting on a web-based tool (like a CDN) and adding it as an interactive link.
Feel your pain with the limited Excel options!