Lisa worked with a pseudonym (5)
I believe the answer is:
alias
'pseudonym' is the definition.
(I've seen this in another clue)
'lisa worked with a' is the wordplay.
'worked with' indicates an anagram.
'lisa' anagrammed with 'a' can make 'ALIAS'.
(Other definitions for alias that I've seen before include "Assumed identity" , "Alternative identity" , "Cabbage salad" , "Also known as" , "A sail (anag)" .)