1)
Why does it say "ki'Dvar Eliyahu"?
1.
Malbim: She made first for him.
2)
Why is it written Hu v'Hi, and we pronounce it Hi v'Hu?
1.
Radak: Either way, both of them ate. Normally, the primary one is put first, e.g. "va'Tdaber Miryam v'Aharon" (Bamidbar 12:1), "va'Tichtav Esther ha'Malkah u'Mordechai ha'Yehudi" (Esther 9:29). Also here, she was primary, even though the miracle came to her via Eliyahu. Malbim - Hashem said that He commanded [His Brachah, so] that she will feed him.
2.
Radak citing Pirkei d'R. Eliezer 33: It is written Hu v'Hi, for they ate in the merit of Eliyahu.
