I found the name (S. Garfinkiel) on the student list, then searched it in the Lodz Ghetto Inhabitants database. 11 possibilities were found, but only one person was born in a year that was possible for S. Garfinkiel's school (School #17B). This seems like it must be the right person, and I have found the full name, birthdate, and addresses for this student (so far).
Additional Comment: I searched for Sara Garfinkiel in the Hospital, Labor, Deportation, and Administrative records, the Lodz Ghetto Labor cards, and I checked the secondary sources, but found nothing. The same thing occurred while reviewing the different sources in stages 3, 4, and 5. I then searched the Lodz Ghetto Inhabitants Database for Sara Garfinkel, a different (yet possible) S. Garfinkiel candidate who was mentioned in the previous reviewer comment. I found that Sara Garfinkel Was born October 3, 1928 (a possible birthdate for school #17B) and that she had two addresses: Brunnen 12 and Brunnen 7 2. I found no additional information on this girl while searching the sources in stages 2, 3, and 4, but in the Oral HIstory Archives AND Catalogue of Survivor Testimonies of Stage 5, I found records of a Sara Garfinkel...the only thing is, she was born in 1920 (therefore not the correct person). No additional information was found. I think the trail may have run cold for S. Garfinkiel, unfortunately.
In order to search more thoroughly for parents and siblings, as suggested in the previous comment, I typed the last name "Garfinkiel" (spelled like the name signed in the book) into the Lodz Ghetto Inhabitants database and clicked through to see if any of the addresses matched the one of the girls I found. After a little while, I got lucky and found Gerszon Garfinkiel, who's birth year seems about right for him to be Sara Garfinkiel's father. The main factor, though, is that the two addresses listed for Gerszon Garfinkiel match the two addresses listed for Sara Garfinkiel. I think these two people were definitely related. This also makes it appear as though Sara Garfinkiel (b. June 27, 1928) is the student who signed her name in the book. I also found Miriem Garfinkiel, (b. 1930)..she had two addresses listed, and the second address matched both Sara Garfinkiel and Gerszon Garfinkiel. Could this possibly be Sara's sister? I'm guessing they are somehow related, but I didn't list Miriem yet since I'm unsure.
Additional Comment: I went back and did the same process of searching for parents and siblings by typing in the last name "Garfinkiel", and I think I have found a possible brother for Sara Garfinkiel. He was born September 26, 1923, and one of his addresses is the same as Sara, Gerszon, and Miriem's. There is also an alternate spelling of the name: Abram Eleazar Garfinkiel...this person has the same birthday (September 26, 1923) as the Abram Elazar Garfinkiel listing. It also has an additional address.
Additional Comment: I went back and searched the names again, and I have found another possible relative..a mother, possibly? Ther are two people named Rywka Garfinkiel, and they both have a matching address for Sara Garfinkiel (although one is listed as Hohens 28 66 and the other is only listed as Hohens 66). The two Rywka listings have different birth years, however..although they are similar. The first listing just says b. 1897, and the second one says b. November 29, 1896. I believe it is more than likely the same person. The two different Rywkas also match the two different Abrams, address-wise. One Rywka's (2nd) address listing corresponds with one of the Abrams' (2nd) address listings. The other Rywka's (2nd) address listing corresponds with the other Abram's (2nd) address listing. This appears to be further proof that the two are related.