Surprisingly, she ran alongside Nazis, showing lack of judgement (8)
I believe the answer is:
rashness
'lack of judgement' is the definition.
'rashness' can be an answer for 'lack' (I have seen 'Lack of caution ' mean 'rashness' so perhaps 'lack' could also mean 'rashness'). I'm not certain of the 'of judgement' bit.
'surprisingly she ran alongside nazis' is the wordplay.
'surprisingly' indicates anagramming the letters (a surprising ordering of the letters).
'alongside' means one lot of letters go next to another.
'nazis' becomes 'SS' (the SS was a Nazi organisation).
'she'+'ran'='sheran'
'sheran' is an anagram of 'rashne'.
'rashne'+'ss'='RASHNESS'
'showing' acts as a link.
Can you help me to learn more?
(Other definitions for rashness that I've seen before include "Recklessness" , "intemperance" , "Impulsiveness" , "indiscretion" , "Impetuosity" .)