just catching up. I wanted to reassure you that I'm sure your sister will not mind that you didn't want to view Miles. In my case my MIL did, my parents did not. That's their choice entirely. Without wanting to sound hard, it really didn't matter to me. I saw him, had photos and his hand and foot prints and that was what was important. Just keep talking about him, make her know he was important to you and a part of the family story.
You could get her a nice keepsake box for her things - there's bound to be something she has that will remind her of him. You could suggest a memorial service or burial - a grave has turned out to be hugely important to us. You could get her a tree/plant which will flower either now or on his due date. And don't forget his due date - it will be tremendously hard for all of you.
I hope this helps.