For that length of time, she should def. get a pre-paid. Have her shop - or do it online to find thebest plan. One carrier (forget which) has a good pre-paid plan that includes cheap calling to U.S.
Of course the best way to call is free over wifi. Use Skype for voice or Skype video talking is good. One place to get pre-paid info is: www.prepaidgsm.net. The sections are broken down by geography. Good forums there.
She does NOT want to use her TM SIM there, unless, literally, you want 4 figure phone bills.
IF she sets her phone to use wifi only - she could use her TM SIM to make calls back to U.S. numbers and do email. If she doesn't do that, she will definitely incur huge bills. Lots of data runs in unknowingly in the background. She will be billed a minimum of $2 on unanswered calls. (You pay for a round trip call to get back to VM.)
GoogleVoice (domestic call forwarding and cheap intl. calls)
T-Mobile lines on unlimited "family" plan - me, wife. Cost is about $80 a line incl. 5GB/mo. data on each line. We have had no landline in 7 years