Two Ways
BLUETOOTH: first of all, if they are large files, do not use BT: the bandwidth is too lean. But, it is simple: make sure that your friend's PB is discoverable: you set that in System Preferences; tell her to set no password, unless she will always have BT on: even then, it is not like WiFi security-wise. Open YOUR Sys Preferences, and make sure that BT shows in the Menu Bar. From the BT menu bar icon, choose "send file". Chosse the file you want to send. Your PB will search for discoverable devices. When your friend's PB shows up, click on "send." Your friend should receive a notice to either accept or deny. She clicks "accept" and the file will be transfered to the folder she has designated as BT transfer recipient.
FIREWIRE:
Much easier: Make sure you have a FireWire cable and your PB is on. Shut down your friend's PB. Connect a FireWire cable between the two PB's. Turn on her PB and immediately press and hold the "T" ket on HER PB. Keep holding it until a FireWire Icon screen saver comes on in her PB. Her PB's hard drive now mounts on your PB as an external hard drive. You may now copy or write files to it to your hearts content.
Blue Tooth is not necessarily fast: remember that. Good Luck.