Righto, 1st I have to be a pedant (sorry) the company is 3 or three I assume as 3g is the technology for connecting you that all mobile networks use.
Also, ask for a deadlock letter as they are not resolving this to your satisfaction. Then you can complain to Otelo.
Further little point that may help you out here, 3 will soon be piggybacking off T-Mobile (and vice versa) as 3's network is so poor and they've had so many complaints! so check here
T-Mobile Coverage Street Check - Mobile Phone Coverage - T-Mobile to see if her coverage will increase soon due to that (I know it's no help at the moment, but may give your friend a little hope that the entire contract won't have zero coverage at her home.)
Hope I've helped! GL!