Isn't she cute? You wouldn't suspect her at all would you? ^-^ I want that coat...
Sometimes when a S.O.P is on a mission they have to disguise themselves as normal people, sometimes going so far as to have to procure different clothing. Slaughter being who she is wears white clothing as often as possible (which is generally 99% of the time) in a world like our where her normal clothes would stand out like a sore thumb she wears this.
As always regardless of the clothing, her sister's bloody hand prints are still on the front.
The thing she's carrying is in fact an art portfolio, it's generally used by people who draw things on giant pieces of paper (like charcoal drawings, pastels, or architecture layouts), then they cover them and role them up to put them inside. Slaughter obviously doesn't have any artwork in there; instead her sword is inside.
That background there is something I found via Google, it's a photo a guy named Ron Reznick took of Florence (or so that's what the description says)I just tinted it blue and added Slaughter's shadow.
(c) Slaughter is mine
(c) the bg photo belongs to Ron Reznick