。
She was so angry she was practically going mad.
Literal
She [topic-は] anger [by-で] mind even go-mad [to the extent of-ほど] was.
~ほどだった ('was to the extent of') conveys the degree of her anger. 気も狂うほど literally means 'to the degree that even one's mind would go mad.' 気が狂う ('to go crazy') is a direct, somewhat strong expression. The particle も adds emphasis — not just upset, but to the point of madness. The overall structure is [cause]で[extreme consequence]ほどだった.