What to say to a friend who has lost a child?

Warning: For those with new babies, don't read this unless you are certain it won't make you worry about your own little one. After my friend went through this, I checked on my daughter as she slept for several weeks despite the fact that she was 11 months old already.

Last June, I attended a baby shower for one of my best college friends. This was her second pregnancy (the first was an early miscarriage) and all was going well! Her due date, which was late September, came and went and she was induced the first week of October. After a difficult labor that ended in an emergency c-section, she delivered a tiny, little boy. He was small, especially for being over 7 days late. After about a week spent hooked up to tubes and monitors, they got to go home as a family of 3. He grew and grew! By his 2 month check-up, he weighed as much as my daughter did at 2 months (and she was an 8 pounder with rolls from day 1).

That's when the nightmare began for my friend and her family. He went to bed in his crib that night after a perfect 2 month check up and he did not wake up the next morning. They had an examination done, and it was labeled SIDS. My friend lives in another state, so I was not able to attend the funeral. I sent a card to her and her husband right away, but have only been in contact with her via facebook as she goes through all of this. Finally, today, just over 3 months after they lost their son, I made it to the post office to mail her a letter, a paper angel from my school (more on that later), and an angel ornament I had her son's name engraved on.

Here is the letter (almost word for word, but a little different because I am typing from my handwritten rough draft, not the handwritten final letter):

Dear ___,
Sometime in January while I was taking down our Christmas decorations, I was trying to think of a way for my family to remember and honor your sweet boy, H. I decided to keep his birth announcement with our Christmas things so we can hang it with our cards every year.

Enclosed is a paper angel that I hung on my school's prayer tree back in December. I just took it down last week so I could send it to you. My entire school community has been praying for you, [her husband], and H. I've also sent you an angel ornament with your little angel's name in it.

Thinking of you everyday, my friend.

Love,
___

My question(s) for all of you: What kind of support can I give her on ordinary days? When his birthday comes in the fall? When the anniversary of his passing comes in December? Whenever I try to talk to anyone about it, I just start to cry. Even after my depression and extreme sadness surrounding infertility, I cannot begin to fathom what my friend and her husband went through and what they are still experiencing.

The situation is not the same, but I found this guest blog post from A Cup of Jo, written by a woman who had a stillborn baby, helpful when thinking of what to write to my friend: 
Motherhood Mondays: I had a stillborn baby

I thought I'd share the link, because this community, more than most, has connections to people with such losses.