The soccer high-flyer joined Lord Sugar's panel last year after Margaret Mountford left the show to pursue studies.
Karren, who was appointed West Ham United's vice chairman in January and was formerly chief executive of Birmingham City, will get her first chance to impress BBC1 viewers on May 12.
She will join Lord Sugar to assess 10 teenagers competing to be named his first Junior Apprentice.
The identity of the teenagers, all aged 16 and 17, is being kept a closely guarded secret until next week.
The winner out of the five boys and five girls will get access to up to £25,000 towards kick-starting his or her business career.
To win the prize they have to get through a series of tough tasks, starting with selling cheese to passing trade and businesses.
The first week is boys versus girls and the winning team will be treated to a meal cooked by Tom Aikens, the youngest British chef to hold two Michelin stars - but someone on the losing team will be the first to hear Lord Sugar's famous words "you're fired!".
Karren will accompany public relations executive Nick Hewer to monitor candidates during their tasks and report back to Lord Sugar.
She has some idea how the candidates feel as she led the winning team on Comic Relief Does The Apprentice, which raised more than £750,000 for charity in 2007.