"主语 + be动词 + so much " 是个固定表达的副词词组用法.
意思是:XX 是如此地~;XX 是这么地~
作用是:作为强调修饰前面的主语(这里的主语就是“Her class”)
Her class is so much fun?
她的课堂是那么地有趣.
◎举几个类似句子的用法供你参考:
He is so much attached to us.他和我们这样的要好.
The news is so much music to our ears.这个消息真中听.
There is so much for us to learn.我们要学的东西还有很多很多.