Being expat with DCs in boarding schools, it is inevitable for them to be homesick especially we are far away from them. Trust me, it takes time, but she will settle, make friends and enjoy her new school.
My DD started boarding at 12 when we were expat in Far East 12 years ago, it was hard for both of us, she was homesick, and mobile phone was not like nowadays, no smart phone for instant messaging. We had to wait for the weekend to talk, and mounted up enormous phone bills.
We went through similar boarding school selection processes, and she had the final decision on the school she wanted to go to. She preferred boarding rather than going to Int'l school. I totally supported that as it was pretty upsetting seeing her saying goodbye to her friends every 2 years as we were moving on to another country.
I do not agreed that voices from home just exacerbate homesickness. I think able to talk to the parents just like normal is very important especially at the early stage, so they don't feel they are abandoned. Also with Skype or FaceTime make it a lots easier now. In those days, during our phone calls she would tell us anything happened in school, people she likes, and people she dislikes, silly things, fun things and annoying things. We would do the same, telling her what happened in our part of the world. It is also important to have quality time when they come back during half term and holidays. You can ask them what they would like to do and involve them in the planning process, sometime a surprise treat works magic.
DD is now a qualified doctor working in London and we still sometimes talked about how difficult it was for her at the beginning of boarding. She said the most difficult things were seeing friends had families visiting for school performances, or games and they got to go home for Sunday lunches. Of course, she missed us, and we missed her, we had a very strong relationship and she certainly did well and we are very proud of her.
Our DS is in the final year of boarding, for him, it was a lot easier, I think with big sister telling him what to do and what not certainly help. It was a lot easier for him to settle in his school.