Eunji left the building with a heavy heart. She didn't want to part with them again but she knew she had to...for now.
This was not the right time for her to reunite with them as if nothing had happened.
The important thing now was that she was able to warn them against her sister whom she had not met yet.
She still had to confront her as to why she was doing this. Why pretend to be her.
She sounded like a broken disk as she repeated those reasons on her mind. To the point of conditioning herself that she could not be reunited with her family unless she had solved her issues.
Well, news flash! Her family might dissappear if she won't hurry up and reunite with them.
That whatever the issues are, they could get through it together as one.
And besides, her original plan of fighting the enemies alone and then come back when everyone was eliminated by her was already no longer applicable since Ana appeared.