I was on Jack Monroe's side in this particular spat until this moment. Anyone who sues for libel over such a trivial remark deserves nothing. I hope she loses.
She's written on Twitter about the effect it has on her of being on the receiving end of consistent abuse on social media from right-wing trolls every time someone in the right wing media attacks her, and I don't think what she describes can properly be called trivial.
According to her, at least, she makes a modest living from her books, enough to support herself and her son while she continues researching and writing her recipes to help people on low incomes (which she encourages food banks to print off and distribute free from her blog, along with the copies of her books she donates) and unless her detractors can substantiate their claims that she makes more money than the PM and is "making a fortune from the poor," then they deserve what happens to them, to my mind.
The problem with our libel laws is that, because libel cases are so expensive and unpredictable, they work in favour of people who can afford to bring or defend them. Jack Monroe is fortunate enough to have a leading libel lawyer who's prepared to represent her pro-bono, so good luck to her. She's risking massive costs if they defend the action and she loses.
What's the alternative -- allow people to make damaging and (if that's what they are) false allegations on social media with impunity?
ETA: I would imagine, based on what happened when she sued Katie Hopkins, she'll be prepared to settle for an apology and donation to a charity of her choice, plus costs. But if they want to fight it, then let's see what happens.