Alright guys,this is my theory as to how it could be Ada.
At the end of re4 Ada retreived that sample for Wesker,right?
Prehaps Wesker used the sample to create this new breed of parasite we see here in the re5 trailer. Ada was last known to be with wesker as far as we know yes? Prehaps after Wesker created this new parasite, he may have put one in Ada too. If you look at the trailer,wesker has the same red eyes as the crow lady,so it could be a possibility right? But I guess we won't find out any more about Ada until Degeneration.