It don't think it'll work there.
It'll probably be using PPPoA tied to a particular phone line and it'll authenticate using the Username/Password supplied by SKY. (not to be confused with the wireless encryption keys)
Sometimes you get the kit through before the ADSL service is enabled on the phone line, but they tell you when it's due to go live in the documentation you receive.
Also, if she's switched supplier then the old ISP should have supplied a migration authorisation code (MAC) which has to be passed to the new ISP so they can enable their service on the local loop.
If they don't have it, then they can't enable their service.
Two ways to get it is by phoning the old ISP or visiting the site below.
http://www.maccode.org.uk/The LAN side isn't really relevant here, the modem (WAN) side is the problem.