Okay, it'll be good for the animators...and who else, exactly? You've got writers to make her lines, a voice actor to perform them, not to mention the scads of programmers having to work toward adding the weight of all that interaction and debugging, and playtesters to make sure things haven't gone awry. No, I'm not saying things will magically fuck up because, suddenly, there's a woman involved. I'm saying that, when it comes to code, Murphy's Law can and WILL fuck you right in the ass, and it especially loves doing it during the crunch time before deadlines. You fix one thing, a dozen break.
Besides, this is all assuming that they don't add new playable characters later as (potentially free) DLC. There's a lot that goes into it, and if memory serves, different parts of large development houses are somewhat segregated. Its no guarantee that an animator will know anything about code or even scripting. They're talking purely from their perspective, and not that of their teammates, who may have a lot more shit to put up with than they do when it comes to adding new playable characters.
Again, I'm just playing Devil's Advocate, and it is possible that they're just bullshitting and adding a woman into the mix is totally feasible and justified in the setting. However, the person who said it'd be too much work may have thought he was talking to a room of people who...well, know great fuck all about actually making this shit. It'd be like Stephen Hawking explaining the physics behind black holes to a room of regular people. They don't know the principles, they don't know the lingo or the jargon, so he'd likely talk in terms he thinks a majority of his audience can understand. Does it always work? Of course not.
