I just found another resource to research the Jews of Latvia - the Latvian Names Project. It is an attempt to do for all of the Jews of Latvia what Edward Anders and his co-workers were able to do for Liepaja - identify the fates of Jews who lived in Latvia before the Second World War. In 1935 the Latvian census recorded 93,479 Jews living in Latvia.
I looked up the name of my relative from Jelgava, Latvia - Sima Schlossberg. She came up on the list, and so did the names of her family - names that she doesn't refer to in her letters to my grandfather. Her sister's name was Miriam, and she was born on August 5, 1909. Sima herself was born on November 27, 1911. Their parents' names were Itzik Ruben and Esther Raschel. Only the possible fate of Miriam Schlossberg is mentioned - in the Riga Ghetto.
Looking back in correspondence from March and April of 2004 (with Miriam's daughter and with a cousin of Sima's), I discover, however, that I do know the fates of the people in the family. Sima escaped from Riga in 1941 with her parents first to Russia and then to Uzbekistan. Her sister Miriam was already living there because she had fled earlier. Sima's father Itzik died in 1942 from hunger. The two sisters and their mother survived the war. In 1942, Miriam married a man named Mikhail Golod, and her daughter was born in 1943 in Bukhara. They returned to Riga in 1945. Sima worked as a bookkeeper, and in 1955 was married to a man named Nohum Bruk and moved with him to St. Petersburg. She died there in 1988, leaving no children behind. Miriam died in 1980 and her mother Esther Raschel died in 1984 at the age of 100.
I'm going to have to write to the Latvian Names Project and give them information on all of these people.