Being a mother and a grandma myself, I can understand you wanting to protect your child,but rest assured that it's absolutely impossible that your friend can be contagious to any one.I would rather tell your friend to be careful not to catch the cold from your daughter...as she doesn't need to fall sick now that she already has enough problems as it is. Take care.
I think I misread your post,,and I apologize.By rereading your post I realized that you were concerned about your friend catching your daughter's cold and not the other way round.You could tell your friend that your daughter is sick with a cold and maybe let her make the decision if she still want to be around your daughter or delay her visit in case her treatment is still ongoing. Good wishes to you all.