For some time I tough it was Alys(Lyla), then because of the same reasons you mentioned I thought it was Alis(PSI).
But now that you people mention that she looks like Ms. Brangwin I think it's Alys again.
Specially because of "her last breath" scene:
Maybe it was a present they gave to fans as an apologise for not including End of Millennium in it.
Alys has not her "crown" like she had when she was buried and the image reminds me a lot of what happened to Nei2nd (in my mind) when she was cloned into Nei3rd and others...
Now, we could say "no doubt it's alys from PSIV, end of the story", but the truth is that we don't really know what were PS_staff's true intentions.
Maybe they wanted a picture of Alis(PSI) but the best they got was Alys from PSIV, because the scene is also similar to the one where Arisa dies (the is picture from PSII, but I think it's meant to represent the scene from PSI where DF kills her and Nero says: “You’ll be reborn to fight for peace again.”). If you watch closely, the hair is a little different at the end... a bit like Arisa's hair (not to mention the purple filter).
Hmmm... ok, the sprite is really from Alys and the AI scenery is very PSfourish... so it was a PSIV-gift from the staff... and they continue to confuse us about Alys(Lyla) and Alis(Arisa).