
"my singleton was up on her feet at about 16 days, very early!"
My singleton was up on her feet very early too (same breed and ours are a breed that are generally slower than pups of other breeds). She weaned early too, as I don't think her Mum had a lot of milk.
I have heard though that it is quite common for singletons not to be up on their feet as quickly as normal simply because they are little puddings due to having the milk bar to themselves. I am sure this is likely to be the case with this pup.
Anyway, hope Willow is now doing well :-).