The 35-year-old star also underwent drama lessons ahead of her appearance.
Victoria was asked to guest-judge on the show following the departure of Paula Abdul, who announced she would not be returning to the series last week.
The former Spice Girls singer admitted her three sons with soccer star husband David - Brooklyn, 10, Romeo, six, and four-year-old Cruz - persuaded her to take part in the show as they love it so much.
She added before filming her part: 'I'm going to try hard to pout and not shatter the illusion that I'm a moody cow, but I don't know if I can. I'm just so happy.'