I haven't read the entire thread, so if I am repeating, sorry, but...
I have a friend who lost her son at 3 months to SIDS. He would have been about 25 right now. She always remembers him. Your relative had the pregnancy to plan for 2 babies, why would she not want to remember the one who did not make it?
Give it to them, if it is too painful now, they may be able to show it later as a remembrance of both twins.
Sorry for your loss.
susan