If you are using a hotmail address, your friend could log-in as you if she had your log-in details, she would then be able to see all your hotmail emails.
Anyone with a hotmail address can themselves log-in on any other computer, as I sure you already know. Just depends if you want to share your log-in details with your friend. Depends how important it is to you I suppose. You could make it a temporary arrangement, but this would mean changing your email address afterwards.