Post: Did Avraham Avinu have a daughter who died the same day as him? This was the question posed to Rav Moshe Feinstein by his student, Rav Efraim Greenblatt of Memphis. His answer can be found ni Igros Moshe, Orach Chaim chelek 4, siman 40, os 6. I present here the original text accompanied by a rough translation. See also the summary over here.
A very interesting analysis, though I won't know how correct it is until I see it inside in the sefer of Maharil Diskin al HaTorah, which I cannot find online. If anyone reading this has access to this sefer, I would greatly appreciate a scan of the relevant page.
As I discussed elsewhere, the derasha appears to be based on the small kaf in this pasuk in parashat Chayei Sarah:
|ב וַתָּמָת שָׂרָה, בְּקִרְיַת אַרְבַּע הִוא חֶבְרוֹן--בְּאֶרֶץ כְּנָעַן; וַיָּבֹא, אַבְרָהָם, לִסְפֹּד לְשָׂרָה, וְלִבְכֹּתָהּ.||2 And Sarah died in Kiriatharba--the same is Hebron--in the land of Canaan; and Abraham came to mourn for Sarah, and to weep for her.|
Without that letter, it means "and to her daughter". There is thus some Scriptural basis. Also, when the Chasam Sofer suggests this, it is not that the daughter died on the same day but that she died much earlier, but the grief over this daughter kicked in at the same time as the grief for his wife Sarah, for reasons he explains. Thus, the death need not be rooted in the pasuk about the blessing Avraham with everything. And as the saying goes, 'Better to have loved and lost, then never to have loved at all.' It is better to have had the daughter, even if she had eventually died within Avraham's lifetime.
We might also raise the related question of placement, which might indeed be part of Rav Moshe Feinstein's question. How could we darshen her death, when we are told of her existence after Sarah's death, in vaHashem beirach et Avraham bakol? The answer to this might well be that, just as the JPS translates it, this is the pluperfect. Not 'Hashem blessed' but 'Hashem had blessed.' Looking back over the entirety of Avraham's life, he had all the blessings. These blessings included a daughter.
There are many other sources to consider. See this post at Avakesh, which lists the sources and puts them into a nice framework, including what textual / peshat difficulty this daughter's death solves.
This is tangential, because it does not feel like there is enough substance to merit its own post. Here is Pardes Yosef discussing this. As far as I can tell, besides citing other interpretations of the small kaf, all he does is cite the Chasam Sofer as well as the Derush Shmuel who say this -- according to Chasam Sofer, that he felt the loss only now, and according to Derush Shmuel, that she actually died on the same day as Sarah:
Be'ezrat Hashem, more later, as I access other sources.