Are the broilers Cornish X? If so, they seem to be more interested in food than anything and there may be no problems. Is the RIR an adult? If too small the broilers will pick on her. Also, you might want to quarantine the RIR to make sure you don't intro disease into your flock. Good luck to you!
I agree with debid. Chickens like to be with a flock. Three should be minimum imo. That way if something happens to one, they still have a companion. Unless your planning to keep it in the house with you!