Rayner was also asked about the resignation of Louise Haigh as transport secretary, after it emerged she pleaded guilty to a fraud offence a decade ago.
Pressed over whether Haigh had been treated fairly, Rayner said she respected her colleague's decision to resign and described her as "an outstanding member of our cabinet".
Asked whether Haigh should accept the £17,000 loss-of-office payment she is entitled to if not appointed to a new role within three weeks, Rayner said "that's a decision for her".
However, she added that if it was within the rules "then I don't see why she shouldn't".