To appear normal - nicely played
Orlov tells Salt she wasn't supposed to get married unless it gave her a tactical advantage.
Salt says "I did it to appear normal."
Marrying him did provide a tactical advantage - his work with spiders gave her a toxin that puts someone in a coma...but does not kill.
"To appear normal" to Orlov, she appears as though she killed the Russian president, shows up back at their hidden lair appearing normal, so she can get inside and lay waste to the lot of them.
Slick.