What is the major obstacle standing in the way of the plan Yasmeen and Amal devise to celebrate Leila's 17th birthday?

In Chapter 31, Amal tells the reader that Leila's 17th birthday is coming up on Saturday and that she and Yasmeen are putting together a surprise dinner for Leila at a restaurant in Toorak. When Amal calls to get Gulchin's permission, however, Gulchin tells Amal that under no circumstances can she allow Leila to go out in public at night, for her reputation will be ruined. With great reluctance and a lump in her throat, Amal agrees to change the location of the celebratory dinner to her own home.