Introducing a Kitten to my 4yr old Calico...?

My mom picked up the kitten after it was hit by a car. She was injured and we took her to the vet. The skin on her bottom jaw was pulled away and it's going to take months to heal. So we don't feel comfortable giving her to a new home until she has completely healed up. She's been here about 2 weeks now. Pumpkin my 4 yr old calico has not been a happy camper. She pretty much stays in my room when the kitten is out and about playing. (Note: The kitten is staying in a spare room and let out with supervision.) They have both exchanged hisses and are practicing avoidance, which is great considering they could be trying to attack each other. They have talked to each other through the door and then hissed and Pumpkin left for the bedroom again. Miracle is about 6 weeks old, and I feel bad leaving her in the spare room but I can't risk them fighting and Miracle winding up more injured then she already is. Any suggestions?