If she is using your account, then Outlook won't allow you to set up 2 of the same names, with same inbox. It makes for a bad fuss. IF she is trying to log into the same account you are, then the server would download the messages to her account, that way any messages she found while she logged in, you would most likely Not see them when you logged in.
If She is using a separate e-mail account, you have to set up all of her acount information separately than yours. You have to go into the preferences of her account and type in her smtp, host, login and pass, separately than yours.