Did you try connecting with a cable?
"'the requested operation requires elevation'" - that means the command prompt should have been run as administrator by right clicking the shortcut and selecting er.. "run as administrator".
The 169 address is just confirming that you haven't successfully connected to the wireless network.
"Is the network card faulty, " - if you connect to other wireless networks without issues, no.
Your sister's wireless router may have MAC filtering enabled, which means it will only accept connections from a list of recognised devices. New devices need to be added to the list. Your laptop may not support the encryption method in use to protect the wireless network. There is interference from another nearby wireless network which your laptop can't overcome (not all wireless network hardware is created equal).