Assuming Windows laptop, run netsh wlan show networks from a command prompt to see what wifi networks are available, their channels and the strength of the signals.
The machine is a Mac. In wondered if this could be a factor, but my daughter assures me that it won't be. She can connect no problem using the WiFi at our house so I guess she's tight about that.
I have suggested she unplugs booster and re-positions it higher up in the house to improve the line of sight.
Blues and Twos, From what I gather now its not being sent via the mains cables, but via direct wifi radiation from the landlords house. It was the "booster " that confused me. Perhaps ATNotts can confirm this
Can confirm it's being radiated not coming down the mains cables.