Dear LEX,
From my own experience I would have to say that YOU are not really truly upset or scared over your step-sister, but that she is resonating the REAL WOUND / FEAR that still lies deep with in you.... use this opportunity to heal your hurt self a little bit more - - - seek and find the real problem, from within.
Please read JILL's story....
http://www.radicalforgiveness.com/content/jill.asp
LoVe,
Rhapsody -