She's no rabid leftist! (7)
I believe the answer is:
mildred
'she's' is the definition.
(I've seen this before)
'no rabid leftist' is the wordplay.
'no rabid' becomes 'mild' (I can't explain this - if you can you should give a lot more credence to this answer).
'leftist' becomes 'red' (red can informally mean communist).
'mild'+'red'='MILDRED'
Can you help me to learn more?
(Other definitions for mildred that I've seen before include "Girl" , "Woman" , "lady?" .)