I am so sorry to hear about your niece. I vaguely remember this episode but can't remember the passage. I am, however, familiar with a lot of passages that are beautiful in time of grief. I wonder if one of them was used for this episode of "Walls of Silence".
You can see a number of them at the following web site:
http://www.ifishoulddie.co.uk/poems.htm
If this doesn't include the one you are looking for, let us know, so we can perhaps help you more in your search. A number of websites give the name of the scriptwriter for "Walls of Silence" (matthew hall). Perhaps the BBC would have a contact e-mail address for him.