My niece is settled during the day but the evening calls home leave her teary

My niece, 13, is staying with me this year while her parents work in another city. School, tuition, friends, all of that has settled better than I expected. The hard part is the evening call with her parents. She is chatty and happy on the phone, and then for an hour after she is quiet, a little teary, and does not want to talk to me. I don't want to cut the calls, they matter to all three of them. Those who have had a child living away from parents, how did you handle the time right after the call? I want to talk to my sister about the routine, so even small things that worked would help ❤️