How do I use a chengyu (idiom) to describe a "one extreme to the other" kind of transformation? In my story, 孔琳's behavior has changed from ultra-depressed to ultra-optimistic in a matter of moments (she has an unstable personality).  Her friends (陈叶 and 胡灵阳) are staring at her in amazement, and I want to write...


  现在陈叶和胡灵阳在一起站着，惊喜地盯着孔琳[chengyu]的变化。


I want to describe this change using a chengyu, but the closest I found was 以耳代目 and 以耳为目 which are variants.  It's not bad (it means something like "substitute ears for eyes"), but I don't think it works grammatically above.  I'm also unsure that the context works here; perhaps it refers to blind people.

Question: How do I use a chengyu (idiom) to describe a "one extreme to the other" kind of transformation?



English derived from above Chinese; only to be used "in case of emergency" (i.e., if the Chinese is incomprehensible):


   Now Chen Ye and Hu Lingyang [are] standing, surprisedly staring [at] Kong Lin's from-one-extreme-to-the-other change.
Depend on what the emphasis is, there are quite a few idioms you can use in this context. 

Some suggestion: 

判若兩人 (like a different person)

前後判若兩人 (like a different person from before)

大起大落 (up and down to the extreme/ high and low to the extreme)

峰迴路轉 (surprising, unexpected)

前後反覆 (change completely from before/ turn 180 degree)

一百八十度轉變 (turn 180 degree)

If you are looking for an idiom 前後判若兩人 fit in this context the best, but 一百八十度轉變 itself is a common phrase