If you have iphones you can send imessages(texts) free over wifi
Same with a Galaxy (message+).
No. If your smartphone/laptop can connect to wifi, you can send messages using apps for free.
I used my stateside phone in Asia to let my spouse know I arrived right after landing. It was like $.50 per text back in 2010. After than, after getting my luggage and through customs, while waiting for my bus, I connected to the airport wifi and got on Facebook. This was using my laptop since I didn't have a smartphone back then. LOL. Within a day, I got a local phone since I was being stationed there. Sometimes you can rent a local phone at the airport. A lot of military just use Skype, ooVoo, Facetime, or other services like a voip device. In 2010, I had a MagicJack that gave me a stateside number my family could call me on while I was overseas and vice versa.
Oh, and make sure whatever device he/she plans to use, that you also plan to take a charger (110/220) that can be used in that country at the airport and hotels.
Two weeks is such a short time, if Verizon offers something that works for OP, I would be inclined to go with that because the person wouldn't have to learn a new phone system, etc. for just two weeks. If it like my Verizon plan, I have an international roaming where it only charges me on the days I am in an international area making calls/texts. Mainly, when we are in Canada which is only once every couple years. But when we spent a week in Niagara, I added it to my plan.
I wouldn't imagine the cell service or wifi would be good in Ireland in the countryside. So she may want to ask more specifically on the wifi options where she will be lodging.
I know on DisBoards on Adventure By Disney, there are some Ireland locals that gave me some great advice when planning a trip to Ireland (haven't went yet) and told me about the roads and lodging, etc. I bet if you ask there, someone could tell you what the Internet service is like where her lodging is.