Can a kallah whose wedding is immediately after Tisha b’av buy new clothes during the 3 weeks?
The issue with buying new clothing during the three weeks is the we don’t say shehecheyanu then. For those who only say shehecheyanu when wearing the new clothing for the first time, (which is the minhag of most people nowadays) it isn’t an issue because she will make the bracha afterwards. Additionally, clothing that we don’t say shehecheyanu when wearing them i.e. new shoes, undergarments, are also permitted. However during the nine days we don’t buy things that will bring us simcha, however there is a special heter for things that are needed for the wedding itself. Also, if it will not be possible to buy them after the nine days it is permitted, because then it is a davar ha’aved.
M:B 551-45, 46, Halichos Shlomo ( Nissan) 14-1, Kovetz halachos 5-6, 12-2,3, 7 ftnt. 6.