Should women say Amen after the Shehechiyanu of Kiddush at the Seder? This is the famous question asked by Rav Tzvi Pesach Frank (Har Tzvi - OC 154 and Mikraei Kodesh Vol 2:35).
The Shulchan Aruch Paskins that women are obligated in the Arba Kosos… four cups of wine... and all the Mitzvos of that evening.
Because if the principle of B’Rov Am Hadras Melech… the glory of The King (God) is in the multitude of people, it is also a Mitzvah for one person to recite Kiddush for the many instead of each one making a separate Kiddsuh. And by listening to the Bracha with the intent one says Amen and fulfills the requirement for sanctifying the day. Afterwards the cup of wine which is the first of the four cups is drunk by all attending, both men and women.
But there is a problem in doing it this way for women. The problem is the Bracha of Shehechiyanu. Most women have already made that Bracha when they light the Yom Tov candles. As such they have already fulfilled that part of the Mitzva. So when the man makes Kiddush and says Bracha of Shehechiyanu and she says Amen, it becomes a Hefsek… an interruption in the Kiddush for her.
Rav Frank unequivocally says it is a Hefsek if she answers Amen. And since there is principle of HaShameya KeOnah, hearing alone even without answering Amen may be a Hefsek too.
Rav Frank adds that one cannot say that this Shehechiyanu covers all the other Mitzvos of the night (e.g. Matzah, Marror, the four cups of wine). Though the Avudraham tells us that it does cover those Mitzvos, there is in fact no Shehechiyanu mandated for them. Were there no Birchas Shehechiyanu being said for the day itself, we would not say it for the other Mitzvos of the night. So the Amen said to the Bracha of Shehechiyanu remains as a Hefsek between the Bracha on the wine, and the drinking of it.
Rav Moshe Feinstein (Igros Moshe OC-Vol.4, 101:1) deals with this issue. He states that even though it apparently would be better for women not to make the Shehechiyanu during candle lighting so they could hear it during Kiddush say Amen and be Yotze then, he advises against it. He reasons that since it is already an established Minhag for her to make the Shehechianu at Hadlakos Neros, it would be wrong to force her to change it. But if she does not have the Minhag established than indeed the preferable way to do it would be to wait until Kiddushm and hear it then.
Rav Moshe further says that telling her not to answer Amen is not an option. Halacha prohibits one from causing others not to say Amen to a Bracha. Answering Amen even when not done to be Yotze the Bracha is A Chiuv Gadol …a major requirement. It is mentioned in Brachos (51B) and this is the Psak of the Rambam (Hilchos Brachos1:5) The Shulchan Aruch (215:2) the Taz, the Tur.
Rav Moshe makes the following argument. The person making Kiddush is obligated to make the Shehechiyanu. And as long as he has to make it, others are required to hear it and answer Amen. Since it isn’t a Hefsek to the person making Kiddush, it isn’t a Hefsek to those listening to it and saying Amen either.
The Shevet HaLevi, (Rav Shmuel HaLevi Wosner) disagrees with the rationale of Rav Frank. He holds that answering Amen is not a Hefsek if there are other Mitzvos specific to that day. So, both on Pesach and on Sukkos a woman answering Amen can rely that it is going on those Mitzvos. But he also does not accept Rav Moshe’s argument either. On Shavuos where there are no other Mitzvos with respect to that day, a woman should refrain from answering Amen to Kiddush if she made a Shehechiyanu at candle lighting.
Moadim U’Zmanim (Rav Moshe Sternbuch) points out that if one was Yotzei in a Shecheyanu, saying it again would be a Bracha Levatalah. So in theory, Amen should not be said either if one said a Shehechiyanu at candle lighting. But he adds that in this case there is a difference since when she made the Shehechiyanu it was not yet night. When night falls, only then do all the Mitzvos of that day apply. Thus she may say Amen at Kiddush and it is not considered a Hefsek.
He also points out that Avraham Ben HaRambam mentions that Yemenite Jews who do not eat bread and had no wine make a Shehakol but still recite the Nusach of Kiddush without Shem U’Malchus (without mentioning God’s name) so that they will not forget the laws of Kiddush. And this is not considered a Hefsek. This apparently means that the only real Hefsek of speech is just talking without any purpose. Amen or even the entire Nusach of Kiddush is not considered a Hefsek
So, it seems that for all of the above reasons, women who made a Shehechiyanu at candle lighting should still answer Amen at Kiddush.
Taken From Torah L'Daas