Genesis 26:35

And they bowed in strange worship, and set themselves to rebel in their evil conduct against Izhak and against Rivekah.

ויקח אשה את יהודית....ותהיין מורת אוח, seeing that Rivkah is reported in 27,46 as becoming fed up with her life if she would have to live to see Yaakov also marry a Canaanite girl, the Torah had to explain what had produced such a prejudice in Rivkah against the local girls.
מורת רוח, the construction of the word מורת, with the vowel patach under the letter ר needs to be understood by comparing it to the root עשה, also a root ending with the letter ה. In Psalms 148,8 we have the formulation ossah devaro, which is feminine, seeing it describes the activity of the רוח סערה, a stormy wind, which is feminine. The construct form of the word ossah there would be ossat, Similarly, the word מורת in our verse is a construct form of the feminine form of the word מורה, not with the vowel segol under the letter ר but with the vowel kametz. [as in numerous similar nouns that appear sometimes as feminine and sometimes as masculine. Ed.] The word מורה meaning being contrary, rebellious, also appears in a slightly different form, i.e. ממרה as for instance, in Joshua 1,18 ימרה את פיך, “someone who will rebel against your orders.” When it appears in a genitive, construct form, it becomes morat. In Proverbs 14,10 we encounter a similar construction (though it is written with the vowel kametz under the letter מ) The verse reads: אבל לב יודעת מרת נפשו, “a heart knows its soul’s bitterness.” The use of the chataf kametz under the letter מ there converts the word from adjective to being a noun. It is derived from מררות, “something bitter.” (compare Deuteronomy 32,32) In our verse here the word מורת is not a noun but a construct form of a verb, similar to Lamentations 1,20 כי מרה מריתי, “for I am experiencing a great deal of distress.” Here (in our verse) the vowel cholem instead of kametz as in Lamentations, is a manifestation of the abbreviated, chataf vowel often found with the middle letter of the root

ותהיין מורת רוח, they became like a razor and a knife, shortening the lives of both Yitzchok and Rivkah. The expression מורת is the same as in Judges 13,5 where the angel told the wife of Manoach that the as yet unborn Shimshon must be a Nazirite and ומורה לא יעלה על על ראשו, no “hair-trimming tool must touch his head.” Even now Yitzchok did not realise the extent of his son Esau’s wickedness. He did not protest his behaviour with a single word. This led to his ultimate error in setting out to bestow the blessing on his son Esau. This, in turn, [i.e. Esau first having been promised a blessing and then not getting it Ed.], led to Esau getting the blessing or advice that he would live (be successful) by his sword. Because of this blessing he hated his brother to the extent that Yaakov had to flee for his very life to another country in order to get away from his murderous intentions.

ותהיין מורת רוח, they angered their in-laws and opposed them in every way. They even reversed the customs practiced by Rivkah in her household.

מרת, a noun, just as מרת נפש in Proverbs 14,10. The root of the word is מרר, embitter, the only difference between the word here and that in Proverbs being the vowel under the letter מ. Here we have the vowel cholem, whereas in Proverbs it is written with a kametz chataf, abbreviated vowel kametz. It is also possible that the root of the word here is מרה, in the sense of Isaiah 63,10 מרו ועצבו את רוח קדשו, “they rebelled, and grieved His Holy Spirit.” This too is a variation of the theme of bitterness. If we accept this word as the root of the word מרת in our verse, the meaning would be that these women actively engaged in causing anger, frustration to Yitzchok and Rivkah. The whole story would then have as its purpose to show how disdainful Esau was of the sensitivities of his parents. He did not even protest his wives’ behaviour or move them out of the patriarchal home.