Thank you KJ. Nicknaming someone 大姐 means she is leader in a team - this was why I thought 大姐 was Ci Ci.
Alternatively, 大姐 describes someone with seniority in the field or being the oldest - hopefully Angela is not the later case
Alternatively, 大姐 describes someone with seniority in the field or being the oldest - hopefully Angela is not the later case