Highly principled old lady ambushed by cur and jerk (8)
I believe the answer is:
dogmatic
'highly principled' is the definition.
'old lady ambushed by cur and jerk' is the wordplay.
'old lady' becomes 'ma'.
'ambushed by' is an insertion indicator (ambush can mean to trap).
'cur' becomes 'dog' (I've seen this before).
'and' means one lot of letters go next to another.
'jerk' becomes 'tic' (I've seen this in other clues).
'dog'+'tic'='dogtic'
'ma' placed into 'dogtic' is 'DOGMATIC'.
(Other definitions for dogmatic that I've seen before include "Asserting positively" , "I'd tog Mac out to be overbearing" , "Opinionated" , "Stating opinions forcefully and arrogantly" , "Asserting things as incontrovertibly true" .)