The independent councillor for Wadebridge East told Disability Cornwall worker Theresa Court that children with disabilities 'should be put down'.
Now, Brewer, who called for euthanasia in order to save money, is facing pressure to resign after the complaint made by Court in 2011 has just been resolved.
Court, who was on a charity stall when the comment was made, was left 'absolutely horrified' and feeling 'physically sick'.
Ordered to write an apology, campaigners have said that it is not good enough.
Katie wrote on her Twitter page: "Colin brewer how would you like to dispose of my son Harvey???
"Many disabled contribute more to society than mr brewer - ask our paralympians xx.
"Shameful ignorance of colin brewer clear for all to see and such beliefs were gone with the nazis or should have been!"
Brewer's letter of apology read: "I am writing to offer my wholehearted apology for the offence these remarks have clearly caused.
"While I meant no offence by my remarks to you I can see, in retrospect, that they were ill-judged and insensitive and should not have been made at all."
Brewer told BBC News he had been trying to provoke a reaction from charity workers in order to start a debate.
He added: "I have no intention of resigning. I don't think I have done anything wrong. I have apologised."
Court told the Huffington Post UK it was "quite frankly an insult that he had to be told to apologise after a year and a half".
She also questioned his genuine regret after the letter was sent with "a second class stamp and folded into no less than eight pieces".