You are right to be concerned about the effect that this conversation could have on your friendship. It sounds as if your friend has had great difficulty hearing anything negative about her daughter.  One thing you could consider is talking to her about specific obvious worrisome behaviors.  Be empathic and tell her you can imagine how frustrating that would be.  Without giving any possible diagnosis, you could encourage her to discuss the behavior with her family doctor or pediatrician.  If the behaviors are as obvious as you believe, that person will be in the best position to either make a diagnosis or begin the diagnostic process.  Your friend is lucky to have someone who is so concerned about her and her daughter.  

Jeanne B. Funk, Ph. D.
Education.com clinical child psychology specialist

This is truly a tough question. I have run into the same situation with a couple of friends. Both had different outcomes. The first thing to consider is how close this friend is to you. Do you have an open line of communication with this friend or is this a more distant relationship? I wouldn't consider making suggestions about a friend's child unless I had permission to do so in the way that I felt like we had an understanding between one another. In addition to that, I would also ask what your qualifications are to make such a diagnosis? Do you have personal experience with this or is this merely something you have read out? Be careful what you suggest here.
 
The two situations that I ran into were both very close friends and I have a totally open line to say whatever I wanted to both of these friends. I am no specialist, other than being the mother of a child with Aspergers and I suggested getting evaluations to both moms because of similar behaviors in our children. One mom completely denied any abnormal behaviors and has continued to struggle through the years with school issues and social issues; the other went in for evaluation and found out that her son was indeed a high functioning autistic and has had success with alternative schooling methods. She brought him home and schooled him through an online charter school. He has flourished.
 
The bottom line here is this: you know what you can and cannot say to this person. Only you know the dynamics between the two of you and whether this will hurt or help. Tread slowly and consider your own limitations and what you might be reading into the situation.
 
You are a good friend to be concerned- just be careful how you approach the situation so that you can continue to be there for this friend.
 
Monique Zarcone
M.A. of Ed in Teaching and Learning