Yes, you're a bit stuffed. There's a 'show characters' box on the security screen for the connection, but you can only see them when you're actually typing in the password - you can't see it retrospectively. You could navigate to the router (usually 192.168.0.1) and change its security settings (if you have the router password), but then your neighbour's going to have no internet connection when *she* gets back.
It's also possible to set up another p2p network between only your machine and the PS3 - I managed it once recently - if you're just trying to get the two to talk to each other? You might even be able to share your laptop's internet connection, but I always had terrible trouble doing that, and it will probably mean you lose your internet while you're doing it...
EDIT - actually, the latter part above is pointless, since I just read again and see the laptop's on the way out...