is that girl in the latest chapter her sister? Do they have a good relationship?

strained bcus their mother treated miyeon better, but miyeon was never cruel to her sister. her sister loves her but maybe resented her in the past due to the unfairness. i think knowing miyeon is sick with amnesia, she treads carefully bcus miyeon forgot about her. :-( but in the recent chapters miyeon seems to start remembering she has a sister