1). Not sure what you mean, she was created by Bern and was able to take part in the game thanks to confirmation that Kinzo was dead.
2). That would be denied by the fact they are seen together with Shannon and or Kanon at seperate times.
3). Erika was likely not an actual person in 1998, just a character to represent the witch hunters.
4). I don't remember the facts exactly, but I imagine that since she had no idea how her 'perfect' logic error was smashed caused her to focus more on that then anything else.

1) I know that Bern would/could place her on the game board. What I'm talking about is the "executed" tip in the 6th game. Did Bern needed a free place and a vessel to place "herself" on the gameboard? But by going with this argument nobody in the story argued that the man from 19 years ago who's an alternate version of Sayo.
IIRC pieces from alternate fragments weren't revived normally. So, that makes Erika (as a character) not originally created by Bern?

2) Well, I don't have the VN at hand now. Yeah the manga showed they were seen together. Mmh I have to search for pages where Erika see Kanon/Shannon. EP6 don't count if Erika hasn't the detective authority.
3) I know she represents witches of truth like how it is showed in the trick ending. But this is new to me. Interesting.
4) It fits to her. But in EP6 she liked to trick Battler by not telling him her moves. At the end losing the duel is what the story demanded.