Somewhat out of the blue, Hopkins wrote asking Monroe if she'd been defacing war memorials. Monroe responded by threatening to sue her.
In a tweet that has since been deleted, Hopkins wrote: "Scrawled on any memorials recently? Vandalised the memory of those who fought for your freedom. Grandma got any more medals?"
Monroe responded by threatening to sue Hopkins after initially asking her to delete the post.
I have NEVER 'scrawled on a memorial'. Brother in the RAF. Dad was a Para in the Falklands. You're a piece of shit. https://t.co/0IGhgT5BoIJack Monroe (@MsJackMonroe) May 18, 2015
Monroe said she would only desist from pursuing legal action for libel if Hopkins issued a public apology and donated £5,000 to a charity of her choice.
Hopkins deleted the tweet and said she was confused between Monroe and columnist Laurie Penny.
Katie Hopkins' most offensive moments
Katie Hopkins' most offensive moments
1/16 Katie Hopkins on 'plus size'
'To call yourself 'plus-size' is just a euphemism for being fat. Life is much easier when you're thinner. Big is not beautiful, of course a job comes down to how you look.'
2/16 Katie Hopkins on naming children
‘I think you can tell a great deal from a name. For me, there are certain names that I hear and I think ‘Urgh’. For me, a name is a shortcut of finding out what class that child comes from and makes me ask, ‘Do I want my children to play with them?’ There’s a whole set of things that go with children like that and that’s why I don’t like those sorts of children. ‘Hi, this is my daughter Charmaine’. I hear: ‘Hi, I am thick and ignorant.’’
3/16 Katie Hopkins on gender equality
'Women don't want equal treatment, they couldn't handle it if they got it. It's a tough world out there. What a lot of women are actually looking for is special treatment. What women need to realise is that they have to toughen up.'
4/16 Katie Hopkins on immigration
'I've always said if you go into a school playground and shout Mohammad, you'll probably get 100 children running towards you!"
5/16 Katie Hopkins to Benefits Street's White Dee
'Do you not feel like the patron saint of druggies and dropouts?'
6/16 Katie Hopkins on tattoos
'Are tattoos just a badge for the stupid? For me, and for lots of people like me, when you see tatoos you think of someone who is just looking for attention, who hasn't managed to find a way in their life through conventional means and who is just shouting 'I want attention! I want to be looked at!'
7/16 Katie Hopkins on addiction
‘I don’t believe what Russell Brand says about addiction. I just don’t buy it. Gazza likes drinking, let him crack on. He is enjoying himself.’
8/16 Katie Hopkins on The X Factor
'The X Factor 2013 has ended in a painful showdown between a fat mum in a jumpsuit (Sam Bailey) and a small boy in whatever his mum laid out for him on his bed (Nicholas McDonald)'
9/16 Katie Hopkins on the Egyptian uprising
'The difference between most mothers and me is that I didn’t sit around drinking coffee at baby group for 12 months after the birth of my baby. No, in three weeks I was back in my suit, back at my desk earning profit for my business and I don’t see why other women shouldn’t do the same.'
10/16 Katie Hopkins on maternity leave
'Egyptian uprising continues to look like Bonfire Night. Protest fireworks. Right up there with angry cup cakes.'
11/16 Katie Hopkins on 'gingerism'
'Ginger babies. Like a baby. Just so much harder to love. A ginger person with tattoos called Jayden? The triumvirate of horror!'
12/16 Katie Hopkins on affairs
'I lied to get someone else's husband because I wanted him. I give myself 8 out of 10 for ruthlessness for that one.'
13/16 Katie Hopkins on the elderly
‘Personally I hate mobility scooters. I find their owners intolerable. Ran past a mobility scooter going up hill. Made me giggle. I need to grow up and stop being an arse.’
14/16 Katie Hopkins after the Glasgow helicopter crash
'Life expectancy in Scotland is 59.5. Goodness me. That lot will do anything to avoid working until retirement.'
15/16 Katie Hopkins on Ramadan
'Channel 4 broadcasts Islamic calls to prayer for Ramadan. A 30 day reminder that minority rules in the UK. Any more PC, it'd be a bloody laptop.'
16/16 Katie Hopkins on self-harming
'I am advised by the Twitterati to 'cut myself'. I grazed myself on my house gate yesterday. Will that suffice?'
Penny had recently been criticised after expressing solidarity with people who vandalised a World War II memorial with "out Tory scum".
Hopkins responded to her remarks.
Penny later said she regretted the timing of her remarks, as it was VE Day, and added that her grandma had been awarded the George's Cross during the war. The medal turned out to be the national commemorative medal for her service in Malta, but Penny said that didn't lessen her pride in her grandmother's achievements.
Despite having confused the two left-wing activists, Hopkins didn't seem too apologetic.