avoid sunlight and moisture
Throw it back to the '90s and go as Posh Spice

Lenin, Medal for defense of Leningrad, Medal for defense of Stalingrad, Medal for Victory over Germany, medals for 20th and 30th anniversary of the Victory over Germany, medal for Victory over Japan, medal for Veteran Serviceman, medal for 30th anniversary of Soviet army and navy, medals for 40th, 50th and 60th anniversaries of the Soviet armed forces, Medal for 250th anniversary of the foundation of Leningrad, medals for 20 and 15 years of service - Irreproachable service I and II class, Czechoslovak War Cross, Czechoslovak Medal for Strengthening Brotherhood in Arms I class, Czechoslovak Dukla Commemorative Medal (1959), Czechoslovak Commemorative Medal for 20th Anniversary of the Slovak National Uprising (1964), Czechoslovak Commemorative Medal - 30th Anniversary of the Struggle for Freedom and Liberation by the Red Army (1974), Mongolia commemorative medal for 30th anniversary of Victory over Japan, Poland medal Victory and Freedom Medal (1945)

Like I said before, it never hurts to have a pair of cat ears stashed away somewhere in case you need a last-minute costume
You can see the dress on her at the link above