You know the bizarre thing is, even if you choose a name that you think is fairly unusual, often loads of other parents think the same thing at the same time, so you end up with the child having loads of classmates with the same name anyway! My parents insist that there were very few Rebeccas around when I was born and yet it's a very common name for women my age!! I like both Sienna and Isabelle, the other thing to think about is how happy you are with an abbreviated version - play around with it and decide if it's going to grate on you if her schoolfriends call her "See" or "Izzy" or whatever.

Whatever you name your baby, she will grow into her name, and even people who might have had some objections will get used to it