What’s the Rav’s opinion on women saying blessings on commandments which they are not obligated in, such as lulav?
The opinion of Rabbenu Tam, Tosaphoth, Rosh and many other Rishonim z"l is that women who choose to perform a misswa from which they are exempt may recite the relevant B'rakha. I subscribe to this view. HaRav SY Kook z"l explained this view as follows: the B'rakha states that "we were commanded", אשר קדשנו במצותיו וציונו, in the plural, referring to Klal Yisrael. Women are of course part of Klal Yisrael, and a woman reciting the B'rakha is describing the eternal relationship between HASHEM and His people as expressed in the Tora and Misswoth. It is a statement of objective reality, and there is no reason that a woman should not recite the B'rakha.