I did not see this the first time I watched and someone pointed it out - at 4:55 minutes you see mom  signing - " I heart you" just before she picks her baby up, this in addition to her apparent distress and disbelief.

Chimpanzees mourn their dead children just like humans
http://www.dailymail.co.uk/sciencetech/article-1352119/Chimpanzees-mourn-dead-children-just-like-humans.html