Can a Buddhist lay be called a teacher elder sister?

No, you are influenced by novels and movies. All Buddhist lay disciples are called "senior brothers" (regardless of gender). Those teachers and younger brothers are not the names of the Buddhist family, but the names of the Wu family and the Taoist family.

What is a "teacher"? Everyone has his own understanding of learning Buddhism, which can bring you enlightenment. Therefore, "being a teacher for one day and being a father for life" is called "father". What is a "brother"? Here, "brother" does not represent gender, but represents "humility and respect for others", so it is called "brother", which is also the concrete embodiment of Buddhism's "equality of all beings"