Don't have much against her personally on account of us knowing so little about her except from the one blurb about eating Versch, - which Augustine almost did too, now that I think about it, this mother-daughter pair sure have good taste, - and whatever she did that made the Tyrant swear vengeance on her, the details of which we don't really know. Except that it maybe involved her siblings? Given what she did to her biological family and that the Shard probably isn't in the habit of having children too often, I'm thinking it's the usual story of unethical experiments gone awry and the sole survivor tearfully swearing to avenge the clones.
Anyway, my reasons for voting Diplomacy aren't complicated. For one, I just want to fight Shard because that sounds rad, and I don't think leaving her behind is a good idea if there's anything we can do about it.