Can you check the laptop and verify that the OS is 32 bit Vista and not 64 bit Vista?
Control Panel, System - System Type.
Also, open OneCare on her system and make sure that the network is configured to be "Home or Work" (configure network on the Firewall tab after clicking Change Settings.) And, if it is "Home or Work" you may also want to check the advanced firewall configuration in OneCare to place a check next to the second File and printer sharing entry, for Internet, on the ports and protocols tab.
-steve