Excel format keeps changing

Does anyone know why an Excel spreadsheet’s format and margins would keep changing from one user to the next? I have a user with a spreadsheet that looks perfect on her machine, yet when she sends it to me via email it looks out of line and everything needs to be adjusted before printing. She uses MS Office 2000 on Windows XP Pro and I use MS Office 2000 on W2K as well. It seems like she’s the only one with the problem. All other spreadsheets I get look fine.