Unless she has an international plan the roaming charges will be a killer and if it's a smart phone the data roaming could wind up costing the price of the trip.
Borrow a phone from your driver, many offer this service, or buy a cheap phone from Digicel or the like. Calling home from Jamaica is considerably cheaper that way.
If she does bring a smart phone, keep it airplane mode and only use wifi so there won't be ridiculous charges.

Bless...
Ed