I like Adelaide best!
I think Adelaide is adorable. However, living in Australia and Adelaide being a large city in South Australia (and in fact, the city where I was born) would be too much like naming my child Ohio :). So I would have to go for Amelia. It's very popular where I live but I think its a lovely, pretty name for a girl. Ainsley is just not my cup of tea, sorry.
Best of luck in your last week of pregnancy!
I love all three of your names for various reasons. In the end, I'd go with Ainsley for its lesser popularity and I don't particularly like the automatic nicknames for the others. However, I really like Lady as a nickname for Adelaide.
My only suggestion for you is Annelise, but it doesn't flow as well with Scarlett.