iphone 7 not connecting to cell towers

My daughter has been having issues with her phone since about a week before Christmas. She has the latest software update on her phone. We took it by Verizon, and they did a soft reset and did something about setting up apple pay, guy said this had been the problem. The phone worked normal for less than a week. Sometimes it picks up a cell signal and sometimes not. She is in the same house with the rest of us and none of the rest of us are having issues. Then last night the phone began turning itself off and on. Need help! She is a busy high schooler and we've come to rely on her being able to contact us as she needs to come and go. Thanks!