Help or suggestions please

我老婆在一公司9年. 前后跟过4个老板, 前边3个都可以, 每次评估得个人2.3 到2.7 (2 means meet and 3 is the highest performance).最后一个老板对她不好 (together in two years), 也可以说合不来,this time 给她一个不好review (1.7), means it did not meet requirement and let her go. she talked to the big boss and did not get any better. if take legal action, any chance to win? any recommendation and suggestions are appreciated.