Kids iphone lost and not in FindMy

My daughter's iphone has been lost at school. Her apple id is linked to mine as she is under 13. I am trying to locate her phone using the FindMy app, but when I log in under either her apple id or my apple id then I only see my device (ipad), not her iphone. Does anyone know how to add her iphone to FindMy so that I can locate it please? I already have her device shared with me i.e. I've done family sharing. Thanks in advance.