i'm pretty sure she was in 0-3 at the time. she got to 3-6 pretty fast, though. she stayed at that size for a while. then 6-9 months at around 4.5 months and grew out of all of those about two and a half months ago and now wears 12-18 months and is 10 months old.
My oldest son wore 0-3 month clothes for all of a month and was fitting into 12 month clothes by the time he was 6 months, he was tall and skinny. My second son wore nb size for about 4 days, wore 0-3 month clothes until he was around 6 months and now at 4 years old he finally fits into 3t size, he's short and skinny. So, as you can see, it can vary quite a bit from one baby to the next, even in the same family, lol.