From the pictures I've seen she was an adult, lol.
Yes, it is taught that she was created physically as an adult.
But, what about her mental capacity?
They never had sex before being expelled from the garden of Eden - why in the world not? Was it part of Eve's lack of development?
Jan 15, 1958 WT p. 63:
Their first act of intercourse that the Bible records was after their expulsion from Eden as sinners. Why they did not have intercourse and produce children during their stay in the garden of Eden is their own personal affair.