After searching M* Ostrowicz, Miriam's was the only name that came up that fit the appropriate gender and age range to have signed the album.
From the looks of it, Miriam had quite a large family, including her father Moszek (b. 1896), her mother Hinda (b. 1895), and her many siblings--some of whom could also be cousins--including Chana (b. 1923), Boruch (b. 1925), Rojza (b. 1929), Bajla (b. 1931), and Gitla (b. 1937). All of this family lived at the same address on Inselstrasse, which is how I connected them.
Miriam had a different fate than the rest of her family in that she was deported on September 12, 1942, on which date there was a deportation to Chelmno. Boruch was deported on April 1, 1942, on which there was also a deportation to Chelmno. The following family members died without listed causes: Moszek (d. June 18, 1942), Hinda (d. May 26, 1942), Chana (d. August 17, 1942), and Gitla (d. March 25, 1942).
Rojza and Bajla are listed with the note PRZ D M 12, which means they could have either moved to that apartment number in the same flat, or that house on the same street. Their fates beyond this note are not known.
There were also two Ostrowiczes who lived at Inselstrasse 17, although the flat number is not given. Chaja (b. 1919) and Menachem (b. 1918) could be cousins. Chaja moved to the Inselstrasse address on August 12, 1942. It is not listed when Menachem moved to the apartment, although he died of unknown causes on May 9, 1942. Chaja's fate is not known.