I am so sorry for your friends and you,,what a inconceivable loss.
I just wanted to pass on some wisdom I have learned doing crisis counseling for suicide survivors..it is so important for your friend to find a safe forum in which to talk! usually families are surrounded with so much amazing support at first, then slowly it dwindles as everyone else goes back to their normal life,,but this families life will not feel normal for so long. Everyone else will start to find it increasingly uncomfortable to hear about the grief, bring up memories, they will no longer know what to say when "I am so sorry" seems done. So they won't bring up " the subject"..
That will be such a key time for you. Ask your friend truly how they are doing,, and allow them time to answer with no response from you..they just may need to talk. Call up with a funny memory of their daughter,, it will be a relief for them to know that she is still real for others as well. Send them the picture you found in your photo album of three years ago, a picnic at the park and their daughter with watermelon juice dripping down her face..or however you can help them feel it is ok, to talk about her, to remember her, to miss her,,that they don't have to just move on to keep everyone else comfortable..
You will be a great support for them..!
I used to work in an assisted living facility, and made it a habit to send a card to the families who had lost one of "my people" at the 6 month anniversary of their death. I would relay a funny story or great memory...Not once did the family neglect to send me a card in return, thanking me for the memory and thanking me for honoring the life that their family member lived. They seemed almost relieved to get my notes,,because everyone else was silent...
I will keep everyone in my prayers..