I mean despite her habits ,it is clear she is a fairly responsible person , the signs being she was for saving the money she won , her way of interacting with her niece etc . I think that's a big part of what sora loves about her too ! , someone who cares and acts on that care even if it involves going out of her comfort zone or any particular need to ,and personal opinion I think sora is the opposite , so she is drawn to tsuki chan and probably considers her her light ,someone who illuminated her dark days(since she was planning to run away from home , it must have been a dark time of her life)