Rashi on Leviticus 18:17/רש"י על ויקרא י״ח:י״ז

1ערות אשה ובתה THE NAKEDNESS OF A WOMAN AND HER DAUGHTER [THOU SHALT NOT UNCOVER] — Scripture forbids this only if the union with the first of these (whether it be the woman or her daughter) came about through a legal marriage. That is why Scripture uses the term לא תקח, the expression employed for "taking to wife in a legal way". Similarly with reference to the punishment for such a union it states, (Leviticus 20:14) "And if a man take (יקח) a wife and her mother, [it is wickedness; they shall be burnt with fire]" — an expression for "taking" to wife in a legal way. But if one has raped a woman he is permitted to marry her daughter (Yevamot 97a).

2שארה הנה means, they are closely related to one another.

3זמה means, an evil plan, as the Targum renders it‎ עצת חטאין , "a sinful plan"; the term is used because it is your evil inclination which counsels you to sin.