You have 2 choices for Photostream for 2 people. You can either share an iCloud account (not recommended!) and not be able to use iMessage since you will both get each others messages. OR you can both have separate iCloud accounts, which means you will have separate photo streams. Now the tricky part. If you are using one PC to manage your photo stream you have 3 ways you can do it.
1) Sign in and out of iCloud whenever you want to change users (not recommended, since it could get VERY messy)
2) set up a second user account on the pc and set up your wires iCloud account on there....this is what I did. Now you can grab her pics and yours, but nothing else gets messed up.
3) set up another iCloud account strictly for photo stream. Set up your primary iCloud account as a secondary and have it sync everything else....set up the photo stream account as the primary and turn on only photo stream. Now you will have your cal and mail and all the other stuff on your main account, and just photo stream on the photo stream account. Now all of your pics will go to your iPhoto.
