We can explain that the Imrei Noam is explaining the opinion of the Rambam and the Rambam paskens like Rebbi Yehuda [as Rabbeinu Manoach Shofar 2-2 and the Shaagas Aryeh 104 prove] that women have no רשות to perform סמיכה on animals and thus there is no value to their fulfillment of מצוות עשה שהזמן גרמא [Rashi goes further and says that they are עובר on בל תוסיף when they fulfill מצוות עשה שהזמן גרמא. We pasken that they do receive reward for fulfillment of those mitzvos]. Hence, it is axiomatic that they have no הנאת משתרשי and we can't say that they accepted the mitzva upon themselves as an obligation because according to Rebbi Yehuda that is impossible.
The problem is that the Rambam writes [Mamarim 4-3] that the only מצות עשה regarding which one can become a זקן ממרא is תפילין. But what about מצה?? Women are obligated to eat מצה so if a זקן ממרא argues with the Beis Din and rules that a piece of matza is invalid and then a man is מקדש a woman with this מצה [which is really valid], anyone who sleeps with her will be חייב כרת. So why doesn't the Rambam say that a psak about מצה can also create a זקן ממרא??
[עפ"י תורת מו"ר שליט"א]
