Sources suggested the London MP had lost her job as Shadow Health Minister because of "loyalty issues" and she herself said: "Ed wanted more message discipline. I'll live; these things happen."
In an online article yesterday, Ms Abbott, Britain's first black woman MP, raised concerns over Labour's acceptance of Coalition cuts, calling on the party to offer "a more far-reaching critique of austerity".
She suggested Mr Miliband should consider scrapping Trident and resist advisers urging him to adopt a tougher stance on immigration.
She said: "I have long despaired of the downward spiral of Labour's rhetoric on immigration."
Ms Abbott said Mr Miliband was "very nice" as he asked her to leave the Shadow post he first offered her in 2010, adding: "I have enjoyed being on the frontbench, but I plan to enjoy being a free agent on the backbenches even more."
Other Labour moves included Fife MP Thomas Docherty becoming a Shadow Environment Minister and David Hanson replacing Chris Bryant as Shadow Immigration Minister, with the latter joining Rachel Reeves in the Shadow Work and Pensions team.