Long-Bailey tweeted an interview with actor Maxine Peake, which made an unsubstantiated claim about US police officers being trained by the Israeli secret services.
The Labour leadership candidate reportedly said she would give Jeremy Corbyn a role in her Cabinet if she becomes prime minister.
Rebecca Long-Bailey and Richard Burgon are close allies of current leader Jeremy Corbyn and shadow chancellor John McDonnell.
Politicians and high-profile supporters of the outgoing party boss have been publicly promoting Rebecca Long-Bailey.
Rebecca Long-Bailey was responding to fresh anti-Semitism claims against Jeremy Corbyn.