第一个可以用and she 换 who,
但是第二个不行,因为 people (who are too stressed out and angry) may have too much yang, 主语是people,括号里的定语从句用来修饰people,may have 是谓语,too much yang 是宾语.
括号的定语从句 who 是在定语从句中充当主语,充当主语时,关系代词who是不能省略的.
只有关系代词在从句中做宾语时可以省略,例如：I don't like the girl [(who) you talked with just now]. who 做talk with 的宾语,可以省略.