Not a Dr, just work from my heart here. The few parents I have been able to talk with have said the same... I try my best to give what she needs and be the best parent I know how to be. The parents themselves end up lost in a world of not knowing what to do. Encouragement for all of them to seek support from a Dr I think would be a good idea. Treatment through counseling.
As far as what can you do for your friend? Be a friend. She may reach a point of feeling she has a full plate. Overwelmed, emotionally drained.
Be there when you can as needed. In my opinion, the words from her heart will give her the needed quotes as needed. The tears do flow. You want to just reach out and make it all stop. The serenity prayer should be stuck on her glasses so she can always see it and remeber... we can only do so much.