Why is it that some are suggesting that because the forthcoming card by Anastasiia features a special costume that it will be a Special Event Card ?
The attached screen capture shows the full set of SECs that have been released so far - I see nothing in those to suggest that because a card features something special that it will be a special event card. It may be, but my guess is that it will not. (The two christmassy costumed cards are not exceptions, in both cases they were not the only such cards offered that christmas).
Because this card would likely sell very well as an ordinary card (maybe with a higher price than normal, as has been the case for previous special costumes) then I think that it will be released that way.