Your sister does not need to meet with them if she does not want to. If she wants to, she needs to be well prepared for the possibility that they are coming to find out if she is still "loyal to the organization," and to measure her response very carefully. Personally, I would make it clear to them that I stood by what I said earlier and saw no need for further discussion.
If the elders want to visit somebody, one cannot know in advance what their motive is, but there's at least a 99.99999% chance that it is not to tell you that you've been a "good girl or boy."
Please keep us posted as to whether she meets with them and what the outcome is.