I'm sorry you have to experience this ! Even if she found your dress offensive , she should have complained to the mall management . She has no right to assault you!
There is no enforced dress code or law that legalize her aggressive act.
Is Qatar changing?
As been summarized in a recent article;
"Though led by a modernizing ruling family, most Qataris are conservative Muslims who practice Wahhabism, an austere form of Islam. Social change that accompanies breakneck expansion is unlikely to sit well with all.
“Qatar is led by a relatively progressive elite that nonetheless has to be mindful of religious or culturally conservative forces within the country. It’s a question of two steps forward, one step back,”
“It’s not easy to be an absolute monarch in this part of the world. Taking everyone with you is going to be hard.”
http://english.alarabiya.net/articles/2012/02/16/194999.html