Participation in a Wedding within Thirty Days of a Sibling's Passing

Can a mourner within thirty days of his sister's passing attend a neighbor's wedding?

The Shach, s.k. 3, wrote to prohibit within 30 days all mitzvah meals, but the Be'er Eytiv and Noda Bi-Yehuda wrote that only weddings are prohibited within 30 days, while other mitzvah meals without joy are permitted. This is the custom. One may participate in a chuppah outside the hall, as written in the Tur, siman שצא: "And Rabbi Yehuda Albarceloni wrote that some enter within 12 months to the chuppah to hear the blessing or to visit but not to eat, and some are stringent not to enter at all, and the Ramban wrote that it is forbidden to enter there at all, whether during eating or during the entertainment of the bride and groom, and so wrote my father, the Rosh, and so is the custom in Ashkenaz that all 12 months stand outside the house to hear the blessings and do not enter the house at all." So ruled the Shulchan Aruch, prohibiting, and the Rema wrote: "And all this in the house where they make the wedding and eat and drink and rejoice, but in the chuppah made in the synagogue, where they bless the blessing of betrothal and marriage, and there is no joy at all, it is permitted immediately after seven (Hagahot Maimoni). And some prohibit until thirty (there in the name of Ravyah), and so it seems to me." And although the Rema wrote to prohibit until after thirty, the Rema speaks of mourning for one's father and mother, for he permits after thirty, and for other relatives, there is no need to permit after thirty, and since we find leniency within thirty for other relatives more than 12 months for one's father and mother regarding the return of a debt of a meal, as explained in the Shulchan Aruch, there, סעיף ב', it seems that all the more so it is permitted within thirty for other relatives.