She has accused TV executives of using it in a 'gratuitous manner' to 'convey a symbolic, subliminal message' associating it with an alleged rapist.
The painting was seen for just five seconds in episode six of the latest series as police searched the home of suspect Ed Burnett, played by Sir Lenny Henry.
But after spotting it, Mrs Hewitt, 64, called in lawyers, who sent a strongly worded letter to Kudos, the makers of the Bafta-winning ITV drama.
They wrote: 'The work features very prominently in some particularly troubling scenes and the symbolism of displaying a cockerel so prominently within the context of those scenes, and indeed an entire television show, centred on the investigation of a rape, cannot be overlooked and is surely deliberate. The cockerel is clearly depicted as connotative of the character whose home it is in, this being someone who is a stalker and suspected rapist.
'You have taken the deliberate decision to associate the work amongst a wide audience with the themes of rape and stalking. This is undoubtedly a derogatory treatment of the work and is therefore a breach of our client's moral rights in the work.'
The framed watercolour is seen as the camera pans across Burnett's living room and follows Detective Sergeant Ellie Miller, played by Olivia Colman, as she walks outside to take a call.
Mrs Hewitt, from the Isle of Wight, who says she has sold thousands of original watercolours over more than 20 years, told The Mail on Sunday: 'I feel my work has been abused. They had no right to use it. They could have easily found me.'
David Tennant in Broadchurch. Photo / Supplied
Asked how she felt when she saw her £125 painting in the scene, she replied: 'Disgusted and appalled. I jumped out of my seat. I was very angry that the programme-makers hadn't got in touch with me. If they had told me the context of the programme, I would have said, "Absolutely not!"'
Mrs Hewitt's lawyers wrote to Kudos in May asking for £10,000 for 'retrospective licence fee, damages for copyright infringement, flagrant damages for infringement and damages for breach of moral rights'.
Mrs Hewitt claims Kudos responded by branding as 'opportunistic' her attempts to settle the situation with a £10,000 payment.
She added: 'I was extremely upset when they accused me of being opportunistic despite flagrantly used my work without permission. This could damage my reputation because it means my work is associated with a show about rape.'
Kudos is understood to have argued that the scene is protected under section 31 of the Copyright, Patent and Design Act, which allows images to be used if they appear 'incidentally' in shots. Mrs Hewitt claims the firm offered her £1,500 on the condition that she sign a confidentiality agreement but she rejected it and is fighting for more.
She added: 'I'm not asking for millions of pounds. I'm only asking for a small amount.'
