Alice + Olivia dress is in Lannister colors. It has a back cutout. She may wear it if Margaery Tyrell has won over the people of King's Landing. Sometimes she uses details from Margaery's dresses.
Christian Siriano dress looks very rich. It's an abstract print but it could be a gold map.
Marchesa two piece when she needs to appear soft.
Zac Posen cape dress isn't something she would normally wear it seems very Cersei.