on both computers go to start, right click my computer, properties, computer name tab, change and give both pc's the same workgroup name.
on your sisters computer go to start, printers, add a printer, and choose network printer.
on your computer, go into my computer, tools, folder options, and uncheck simple file sharing (I think it's at the bottom usually). Then apply and go to your music folder and right click, go to sharing and security, choose share this folder and add a share name.
go back to your sisters computer, go to my computer, my network places, choose view workgroup computers (on left), double click your computer (desktop)'s name, right click on your shared music folder and choose map network drive. Assign the network drive any letter and make sure reconnect at logon is on, then hit ok to save changes.
Now to get to your music all your sister has to do is go to my computer and click on the drive you just made (whatever you called it, z:, h:, etc.) I usually right click on the drive and send to desktop to create a shortcut for it. Let me know if that doesn't work.