Chyenne and- Sky

Barked: Sat May 24, '08 4:55am PST 
I have a question.My 5 year old husky(sky)is being treated for heartworms and she is in the same fence as our 6month.She is showing signs of aggresion toward chyenne(6 monyh old).She wont play with her,just fight if she gets to close.
IS THIS NORMAL?If anyone can help me,I would greatly appreciate it.
signed Jeany