When women say the Schehechayanu blessing when they light candles for festivals, should they say amen to the Schehecheyanu blessing during kiddush? Is this considered a hefsek? What about on a day such as Rosh Hashana where the Schehechayanu blessing is considered a safek by many poskim?
Your question is a scholarly one and therefore I am immediately referring you to sources where you can study the issue on your own and I will only give a short summary of the issues. In regard to the "Hefsek" for women who have said Shehechiyanu, see Shmirat Shabbat Kehilchata Vol.II, Chap. 44:4, note 17. In regard to Rosh Hashana see Shmirat Shabbat Kehilchata Vol.II, Chap 47 note 218 where most of the sources on the issue are quoted. In regard to Shehechiyanu said by women by candle lighting for festivals,this may come as a surprise to many but the Mishna B'rura (סימן רסג ס"ק כג) actually suggests that women refrain from saying Shehechiyanu by candle lighting. This is based on the She'ilat Yaavetz who said there is no source for this practice, but he also says that women who do so should not be rebuked. After having said Shehechiyanu at candle lighting, they should therefore not answer Amen to the Shehecheyanu by Kiddush since it constitutes an interruption. (See Shmirat Shabbat Kehilchata Vol.II, Chap. 44:4). However, as known in many households saying Shehechiyanu at candle lighting has been the practice for many generations and it appears in many siddurim. Now the question arises do we tell them to stop the practice and do we start telling women not to say amen after a "bracha". The She'ilat Yaavetz 107 said he did not stop his wife from saying Shehechiyanu at candle lighting. Rav Moshe Feinstein zt"l (אגרות משה או"ח ח"ד, קא ) says that the women answering "amen" after Shehechiyanu at Kiddush does not constitute a "hefsek", for this has been the practice for hundreds of years and would it actually be a hefsek women should have been rebuked and told to discontinue. Furthermore, he says that telling people not to say amen can be detrimental. (See also שו"ת רבבות אפרים ח"א סי' קפב ) On the other hand, Rav Feinstein zt"l also says that where there is no such practice, women should not begin to do so. In Luach Eretz Yisrael of Rav Tokatchinsky zt"l it says that women say Shehechiyanu at candle lighting. Although, he does quote the reservation of the above Ya'avetz in parenthesis, he did not forbid the practice. The Aruch Hashulchan 263:12 also says that the practice of our women is to say Shehechiyanu at candle lighting and they are not to be rebuked since they usually light the candles right before Yom Tov and the Shehechiyanu is meant for the Yom tov and not the candle lighting. However, Rav Ovadia Yoseph Shlit"a in Yechaveh Da'at 3:34 rules that women should discontinue the practice of Shehechiyanu at candle lighting. In regard to Rosh Hashana, the Shulchan Aruch (600) rules that Shehechiyanu is to be said at Kiddush on the second night. It is therefore not a hefsek. Placing a new fruit is only a chumra in order to satisfy all opinions.