WPA and WEP are 2 different types of encryption on your wireless. WEP is the easiest to configure. What you do is type in a passphrase, it will make a WEP Key.
On her client you can configure the SSID, WEP encryption and say Key1: xxxxxxxxxxxx. The key is a hash of that passphrase generated.
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About her not being able to connect...is that because she can't see the Access point on her list?(if you were broadcasting the SSID?) Or she can connect to your AP but unable to get an IP issued by the DHCP server? Make sure TCP/IP is set to Automaticly Obtain on the wlan0 card.
If you put in WEP encryption make sure that is correct and you have the correct channel and SSID set on your cardconfig. If that is all correct you should be able to ping hosts on the same subnet. (Default addressing scheme for linksys is 192.168.1.1/24 or subnetmask: 255.255.255.0) If you are running windows xp, turn off the windows firewall on machines if you want to ping eachother. Windows Firewall blocks ICMP on default.
** Also if you have wireless mac filtering ON and didn't add her MAC address to the Access list that might also be a problem. This will allow only the MAC address of the cards you put in to access the AP. If its on, put her MAC address in there. (Physical Address when you do a ipconfig /all on winxp, 2k.)