The Kli Yakar offers another wonderful explanation. In the Pasuk תָ הּ כּ ֹ ָבֹא אַבְרָהָם לִסְפֹּד לְשָׂרָה וְלִבְּ וַי, the word לְשָׂרָ ה is inserted between the connected phrases; it should have said לִסְפּ ֹד וְלִבְכּוֹתָהּ לְשָׂרָ ה. Additionally, the entire phrase seems redundant, as it could have simply stated לְסוֹפְ דָ הּ וְלִבְ כּוֹתָ הּ. Furthermore, usually, weeping precedes eulogizing, but here the order is reversed, as in most places weeping is for three days and eulogizing for seven. He explains that with most deceased, the mourning diminishes over time because eventually everything is forgotten. However, this righteous woman was missed more each day due to the absence of her Torah and good deeds, which were lost to her generation. Therefore, the eulogy preceded the weeping. Furthermore, the Kli Yakar adds, Chazal said (Sanhedrin 22b) that anyone whose first wife dies, it is as if the Beit Hamikdash was destroyed in his days. Therefore, Avraham initially came to eulogize Sarah for her sake, but he did not weep for her because he knew she ascended to a lofty and noble place, more so than she had been in this dark world. Afterwards, he wept for the Beit Hamikdash that was destroyed in his days, as even the angels of peace weep bitterly for its destruction. Therefore, the word לְשָׂרָ ה is inserted because his weeping was as if the Beit Hamikdash, which was 100 cubits high, was destroyed in his days. Hence, the small letter kaf alludes to this idea: when the letter kaf is written in its full form (כ״ף), its letters total one hundred (20 + 80 = 100). This hints that those hundred cubits – symbolizing Sarah’s full stature and perfection – were now reduced and made small. It is a precious insight noted by the Kli Yakar.
Another explanation, also found in the Kli Yakar, is that the small kaf hints that she died ב ּ ְ ע ֶ ט ְ י ו ֹ שׁ ֶ ל נ ָ ח ָ שׁ – due to the serpent's counsel, which caused death to Adam, who was created from one end of the heavens to the other, and due to the serpent's sin, he was diminished and set at 100 cubits: וַתָּשֶׁת עָלַי כַּפֶּכָה – You have set Your hand upon me, (Tehillim 139:5) where kaf means 100. Since he was diminished and set at the number kaf, his strength weakened, and he became susceptible to death.
