For those who have the custom that everyone make kiddush at the seder, what should the women do about havdala this year. Do they say the whole nusach of havdala? If not, how can they be yotzei by listening to that part, isn’t it a problem of trei kolei lo mishtamei?
In truth your question would also apply to borei meorey h’aish, which is also controversial if they have to say it or not. Those who have the minhag that even the women say kiddush may say it even when the seder is motzei Shabbos and the havdalah is not considered a hefsek. The reason is because essentially women do have an obligation to say havdalah, (and borei meorey haish) and if there is no man to be motzei them they will say it themselves. Additionally even according to those who say that they don’t have an obligation to say havdalah, however the M:B (296-35) says that they may act as if they do have an obligation, (similar to any mitzva that they can do voluntarily) Therefore, saying havdalah is not considered a hefsek, because they also have this obligation.
As a side point, although women usually don’t drink from havdalah, this year at the seder it is permitted, because the cup is also kiddush.
M’bais Levi 18 pg. 21, Shmiras Shabbos Khilchoso 62 ftnt. 27in the name of R’ S. Z. Auerbach zt”l, Shulchan Shlomo 296-11(b).