Corrected entry: Anna is a vampire as well as her mom. It shows flash backs to when her mom was young and friends with Katherine. She was a vampire at that point already. In a few episodes after that it tells us that a baby has to be conceived before a women turns into a vampire. This does not make sense because Anna was conceived after her mom was a vampire.
Corrected entry: Bonnie uses some magic, a map and Jeremy's blood to try and locate the captured Elena. She states that, because Jeremy and Elena are blood-related, the spell will work. However, we know from previous episodes that Elena was, in fact, adopted and is not blood related to Jeremy. The spell, however, still works and they find Elena's location.