can any1 help me... iphone 4s wifi...

[gareth...]

hi can any 1 help me. im new to this so dont no if im posting this in thr right place...
my partnes has a iphone 4s and she cant connect to wifi unless her phone is next to the router...
i have a iphone 4 and i can pick up the wifi fine on my phone and other local wifi networks so im guessing its her phone...
can any 1 help me please shes doing my head in now lol