Different versions of Excel

Hello everyone, I have a problem, which seems like a small problem, but it is impacting on the quality of work.  I compile spreadsheets for my manager.  Where I would put a fraction (eg. 0.25), I use a comma and all my formulas work 100%.  But when my manager opens the file on her side, she gets an error message in the total column wherever I have used a full stop in my fractions.  For her documents to work, I need to change it to a comma.  I would assume it is because we have different versions.  Is there an easy way around this?

Thank you, from a very beautiful day here in Cape Town, South Africa!