Namely only these three acts have participated in the Eurovision song contest FOUR times. (If I am missing someone please correct me in comments!) A special mention goes to Lys Assia who has participated in three years with four songs, and in three consecutive years just like Valentina until now (and Udo Jürgens for the matter). Not forgetting Elisabeth Andreasson; three times in various duets but only once as solo, for two countries.
Fud LeClerk sung for Belgium in 1956 (Messierus les noyés de la Seine), 1958 (Ma pètite chatte, 5th), 1960 Mon amour pour toi, 6th) and 1962 Ton nom (13th)
Peter, Sue & Marc sung for Switzerland, and every time with a different language! in 1971 (Les illusions de nos 20 ans, 12th), 1976 (Djambo, Djambo, 4th), 1979 (Trödler & co., 10th) and 1981 (Io senza te, 4th)