1)
What is the meaning of "Bazah"?
1.
Radak: This is past tense (scorned); the middle letter of the root (Buz, i.e. Vov) is omitted. Here the accent is on the last syllable; in this conjugation, usually it is not. Malbim (Yeshayah 37:20) - they scorn you, for they know that you will fall here!
2)
What is "Besulas Bas Tziyon"?
1.
Radak citing Targum Yonasan: The kingdom of the congregation of Tziyon. It is like a virgin that was not overcome. Whenever 'Besulah' applies to a nation or congregation, it means like this.