Behind the scenes or otherwise, she really didn't do that much.
Sure she contributed money and was infatuated with Wesker, but beyond that, she was just along for the ride. Irving contributed money as well, "research like this doesn't fund itself...yet everyone looks down on me", yet he had a larger role I think, with being seen more, as well as him pretty much being the reason Chris & Sheva progress, as they are trying to catch Irving...
Excella was cool and all, but her role was insignificant, and I feel that she could have survived and had a role in a future game, as she is introduced and killed off pretty quickly. They could have used Wesker to introduce her, then with Wesker being dead, she could still have shown up, now she & Wesker(and Irving for that matter) are dead, leaving no one to take up the antagonistic role, except maybe Nicholai....