Hey, why don't you let someone who knows what he's talking about up in here?
:: pats "Professor" Icepick on the head and scoots him outta da way ::
There is a VERY SMALL, PRECISELY LIMITED amount of memory allocated for loading all the frames that characters keep around when they aren't on point - hitstuns, standing, falling, jumping, their assist action etc. Win poses do not fit into this amount of memory because you'd need to load all poses for all 6 characters.
There is a much larger amount of memory allocated for holding all the rest of the art for two characters at a time - each team's point. In this goes everything else, including win poses. All win poses for two characters can be part of that because you don't have to load 'em for the other four.
This is the same reason we don't have 3x same character on all teams: the memory allocated for assists is the memory for the six largest assists in the game with a maximum of two per character - say Merry Go Rilla, Titan Knuckle, Hornet Bomber, Cilia Slide, etc. Let's say those are 100, 90, 80, 70, 60 units of space. If Cerebella's third largest assist is bigger than Hornet Bomber, say 85 units, then allowing 2x Cerebella on a team could run the game out of memory if they choose MGR/Titan Knuckle/3rd largest/Hornet Bomber on down, by requiring 100+90+85+80+70+60. Now I never have to explain any of that again!
As long as Eliza is smaller than Big Band and Cerebella (and she will be, those two are GIGANTIC), she'll fit on console and win poses have nothing to do with it.