If an Arusah made a Neder and the Chasan died the father is given the right to annul the Neder. (1)
If the Chasan heard about the Neder and died the next day or the Chasan affirmed the Neder and then he died the Neder may no longer be annulled.
If an Arusah makes a Neder and she divorces and receives Kidushin from someone else on that day, the father and the second Arus may annul the Neder together. (2)
Once the father hears about a Neder it may only be annulled on that day.
If a woman makes a Neder and her Chasan divorces her and remarries her on the same day he may no longer annul her Neder.
A husband may not annul Nedarim that were made prior to the marriage.
The day before the daughter of a Talmid Chacham marries it is common for the father to say that all of his daughter's Nedarim shall be annulled. (3)
The day before a marriage it is common for the Chasan to say that all of the Nedarim of his Kalah shall be annulled. (4)
Rami Bar Chama asks whether a husband or father may annul a Neder without first hearing about it.
If a husband says that all of the Nedarim that his wife makes before he returns from his trip shall be affirmed it is not valid.
If a husband says that all of the Nedarim that his wife makes before he returns from his trip shall be annulled, it is valid according to Rebbi Eliezer.
Rebbi Yoshiyah says that a husband may not appoint a Shali'ach to annul the Nedarim of his wife, but Rebbi Yonasan argues.
A BIT MORE
1. The father may annul the Neder whether the Chasan heard about the Neder and dies that day, or the Chasan did not hear about the Neder at all, or if the Chasan annulled the Neder.
2. Even if this repeats itself 100 times on the same day the father and the last Arus may annul the Neder together.
3. Once she is married the father no longer has the right to annul her Nedarim.
4. After the marriage the husband may not annul Nedarim that were made prior to the marriage.
A husband may not annul Nedarim that were made prior to the marriage The Rashash says that although a husband may not annul Nedarim that were made prior to the Erusin however any Nedarim that she made during the Erusin may be annulled by the husband after the Nisu'in.
If the father heard the Neder of his daughter and annulled it but her Chasan didn't hear about the Neder until he married her the Neder may no longer be annulled. Therefore it is the Derech of Talmidei Chachamim to tell [his Arusah] prior to the Nisu'in that I am annulling all of the Nedarim that you made after the Erusin. A father should also tell his daughter before she leaves his house that I am annulling all of your Nedarim. (Shulchan Aruch YD 234:10)