When Jun didn't respond to her little cry for help Rachel acted in out panic, growing her fangs the hybrid shifted slightly then bit down into Archer's arm hard fangs sinking into Archer's flesh. Rachel wasn't going to let this woman do what she wanted her her, and she wasn't going to let Archer touch her like this either. If Jun wasn't going to help then she would have to do what she can do and that is to bite Archer.