First off, BT phone and ADSL / Dial-Up to the Internet
- OR -
Cable (NTL, Telewest) and Cable Modem with USB / LAN connection?
If the wireless connection is from a router only, then I assume that the internet connection is plugged directly into the main PC or is the internet wire (from the phone) connected to the router too (ADSL connection)?
If the first instance is the case then there may be some settings to be changed on the router..
Otherwise, your friend will need to make sure that she has "Internet Connection Sharing" enabled on the main PC.
This Link should give you the information to do that.