how would i go about installing those, if not through cydia? Thank you
Sorry for the "how do i go to macthemes" i thought it was through Cydia and not an actual website.
I'm going to do a nutshell answer and you need to search out the details.
Once you install Winterboard there is a folder in your phone's OS (you won't see it on your springboard) located at Library > Themes.
Download a theme from MacThemes and make sure it is called Name.theme. Inside is a folder called Icons. Your theme icon PNGs go in there and they have to match the icon's name on your phone. If you want to change them you rename them, for example SMS used to be called Text but to work on 3.0 it has to be named Messages.png. Wallapaers go on the same level as the icon folder. The info.plist file control things like font size, color and position. Thats used for making icons invisible, a different color or changing the calendar date size for different icons. You can add icons to an existing theme by sticking them in the Icons folder.
Just download one of the prominent themes and see how they do it.
Use iPhoneBNroswer/PC or PhoneView/Mac to upload your theme folder to the Library/Themes folder on your phone. Those two apps mean you don't have to mess around with sFTP, just have the phone connected to your computer. You won't have to install OpenSSH or anything else as long as your phone is jailbroken.
Launch WinterBoard and you should see you theme listed, select it and hit the home button.
Google for more detailed info.
Teach your girl how to do this as it can be very time consuming.