Hi Aarizkx, there's no subjunctive mood in either of your sentences. There is past perfect (or pluperfect) - "hadn't been", simple past - "wasn't", and past conditional (or perfect conditional) - "would have gone".
Note that we don't normally use the word "hypothesis" in connection with conditionals that involve a hypothetical situation.
Your first example is an instance of the third conditional. It describes a situation in which the meeting took place in the past, and attendance was in fact mandatory, but discusses the hypothetical (unreal or counterfactual) situation in which attendance was not mandatory.
The second example seems to be an incorrect version of the second conditional. If it had been written correctly as "If attendance at the meeting weren't mandatory, she would just go home", this would describe a situation where the meeting is in the present or future, and attendance is mandatory, and would be discussing the hypothetical situation in which attendance is not mandatory. Here, "were" would be a subjunctive.