Both outfits sound adorable.
My only concern (and I may be over-thinking this) is that KS may upstage the birthday boy in either outfit. KS is a gorgeous yorkie, and in a darling outfit, she will attract all the attention. It's Amon's big day, not KS's. If it was KS's birthday, she could wear the prettiest outfit, and attract all the attention. That would be perfectly okay, but that's not this situation.
Perhaps KS could wear a nice party dress, but not her fanciest ones?
Again, I may be over-thinking this. Feel free to ignore my post, if you think I am.