I don't know how she did it but I have a user who is sending mail and the sent items are being stored in the sent folder of a user she has proxy access to instead of her own.

I thought that she was maybe replying to messages in a shared folder but that is not always the case. There are messages that are her name with her name in brackets and some that are just from her. and of course some that are from the user she is proxied too with her name in brackets.
How could this happen and how do I get her messages back into her sent folder?

the two users have several shared folders as well as proxy access.