When is your mother's birthday?

Her birthday is in June在某一年/月,用介词in;
or
Her birthday is on June 9th.在具体某一天用介词on.
祝你开心如意!那her bithday is June 9th对吗？不对！【在六月九日】就属于【在具体的某一天】，要加介词【on】才对。