We learn from Sanhedrin 67a that (man or woman) the punishment for sorcery is death by stoning.
Most punishments in the Torah say "מ֥וֹת יוּמָֽת"- "shall be put to death" by an aveirah that carries the death penalty.
Why for a sorceress does the Torah phrase it as "לֹ֥א תְחַיֶּֽה" - "shall not live?"
Rather than command us to put witches to death (just like any other death penalty in the Pentateuch) the bible here instructs others (perhaps the courts) to not let any witches live, which seems to be a simple translation of this verse from Hebrew to english.
Rashbam notes that this must be a specific instruction given to others to "hunt them down", because witches tended to practice witchcraft in hiding. Shadal follows this understanding as well.
(Various other Jewish commentaries suggest that this language is used to teach us that the commandment is to kill witches immediately however possible, as opposed to waiting for judgment.)
Mecklenburg suggests that this wording is used as a parallel to Deuteronomy 20:16, which refers to the killing of all of the Canaanite Nations, and tells us that we should not have mercy, even on women. This applies here as well, where the verse is discussing witchcraft, which was generally performed by women.
In contrast to the authorities in the previous post, Rabbi Joseph H. Hertz, former Chief Rabbi of the British Empire, in his Chumash The Pentateuch and Haftorahs states:
The wording of the command is in an unusual form. We should have expected 'A sorceress shall surely be put to death.' Some commentators, therefore, explain it as a prohibition against resorting to the sorceress, and thus enabling her to thrive in her nefarious avocation.