Why does it say "Teshalechnah"?
Radak: Sometimes there is an extra Nun-Hei at the end of a word, e.g. ha'Misderonah, ha'Parshedonah (3:23, 22), even though this is not common at the end of a verb.
Radak citing his father: It refers to sending both of her hands 1 - the right for the hammer and the left for the peg. The verse attributes Shelichus to the hands, for they do the action.
Radak citing his brother: The Shirah justifies why Ya'el is blessed so much. Other women 2 , do they send their hand to the peg like Ya'el did?
In Biblical Hebrew, the feminine plural often ends in Nun-Hei, e.g. va'Tipakachnah, Hazenah, va'Tomarnah (Bereishis 3:7, 4:23, 31:14). (PF)
What is "Lehalmus Amelim?
Rashi, Metzudas Tziyon: It is to strike Sisera 1 , who was weary.
Radak: It is a smith's hammer.
Malbim: [One hand held the peg, and the other,] the hammer. [Her hands were] weary [due to her weakness]. Sometimes "Yad" is masculine - "Yad... u'Vo" (Yechezkel 2:9).
Malbim: If Amelim refers to Sisera, why is it plural?
Why does the verse elaborate about what she took to kill him?
Rashi (Nazir 59a), Targum Yonasan: She did not kill him with a weapon, due to "Lo Yihyeh Chli Gever Al Ishah" (Devarim 22:5).
What is the meaning of "Machkah"?
Rashi: It is an expression of carving [into his head]. Malbim - it was a very small dent.
Radak: She removed. This word refers to removing excess piled above the top of a Kli of a known measure. (Bava Basra 89a)
What is the meaning of "Machatzah"?
Shemos Rabah (15:22): It is an expression of killing.
Rashi: It is an expression of striking.
Rashi (Bamidbar 24:8): It split it.
What is the meaning of "v'Chalfah"?
Rashi: It passed through from one side to the other.