You can do it without any "account details." But you need a computer that runs iTunes. Just plug it into a computer that has iTunes running and do a Restore on the iPod. This will erase the iPod, re-install its software, and set it to default settings.
There is one potential problem, if this really is a 3rd gen iPod from 2003. Does it have a touch wheel (not a click wheel) with four playback touch buttons in a row that glow orange when the screen backlight comes on?
If that's the iPod model you have, it is designed to work with a FireWire connection, not USB. It has the standard dock connector, but it cannot charge using a USB connection. If your sister has a Mac (or Windows PC) with a FireWire port, it should work fine with the latest iTunes. Otherwise, it may be a problem.