Normally there will be a number of phone service providers that specialise in long distance calls. Some of them you can specify the country that you wish to dial regularly so you can get additional discounts on those calls (at the expense of calls to other countries usually). Her best bet would be to ring around to all the bigger telcos and see what they have to offer (AAPT, telstra, optus, primus telecoms are those who come to mind off hand).
HTH.