When infected by it, her underlings got the bleach (8)
I believe the answer is:
whitener
'the bleach' is the definition.
(synonyms)
'when infected by it her' is the wordplay.
'infected by' indicates putting letters inside.
'her' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'when' enclosing 'it' is 'whiten'.
'whiten'+'er'='WHITENER'
'underlings got' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for whitener that I've seen before include "Powdered coffee additive" , "Blanco" .)