Then I guess it depends on exactly what the error message states.
Also, as I stated above... If she setup an access list on there router then you need to ask her to add your phone's MAC address to that list. You will only be able to access the WiFi if you meet two conditions:
1. You know the password. Which you do.
2. Your phone's MAC address is part of the access list.
To find your phone's MAC address the generic steps are as follows (it may vary from phone to phone):
1. Settings
2. About Phone
3. Hardware Information
4. Scroll down until you see WiFi MAC Address, MAC Address, or something similar.
Note, you must activate your phone's WiFi in order to see the MAC Address.