She made her debut in the first show of Series 20. She won her first four games before losing to Andrea Parker 43 – 30, but these four wins were enough to earn her a spot in the final rounds as #7 seed. She beat Billy Ward and Fiona Willis on her way to a grand final showdown with #1 seed, octochamp Derek Coombs. With the score 67 – 66 in Barber's favour going into the crucial conundrum, it looked to have slipped away from her when Coombs buzzed in on 18 seconds. However, his guess was incorrect, and when Barber's guess on 26 seconds also proved incorrect, the final score was confirmed at 67 – 66, and Barber became the twentieth champion of Countdown. At the time of her victory, Barber was 60 years old, also making her the oldest Countdown series champion to date.
Barber also returned in 1996 for the Supreme Championship, but was again defeated in the first round, this time by Series 27's Richard Campbell. She took the lead briefly after spotting MASTERY, but Campbell beat her in the next letters game to even up the score. However, Barber messed up her solution in the final numbers game and Campbell unravelled SILVERCUE, leaving him to beat her 59 – 37.
|#||Date||Type||Contestant 1||Score||Contestant 2||Guest||Lex||Max|
|1004||3/07/1990||P||Liz Barber||58 – 33||David Morris||Richard Stilgoe||Della Thompson||73|
|1005||4/07/1990||P||Liz Barber||54 – 29||Bill Giles||Richard Stilgoe||Della Thompson||74|
|1006||5/07/1990||P||Liz Barber||46 – 32||Sue Goodworth||Richard Stilgoe||Della Thompson||70|
|1007||6/07/1990||P||Liz Barber||33 – 23||Anne Duncan||Richard Stilgoe||Della Thompson||73|
|1008||9/07/1990||P||Liz Barber||30 – 43||Andrea Parker||Richard Stilgoe||Della Thompson||73|
|1062||21/09/1990||QF||Billy Ward||28 – 61||Liz Barber||Simon Williams||Simon Mason||83|
|1066||27/09/1990||SF||Fiona Willis||37 – 50||Liz Barber||Tim Rice||Simon Mason||70|
|1067||28/09/1990||GF||Derek Coombs||66 – 67||Liz Barber||Tim Rice, Gyles Brandreth||Simon Mason||124|
|1068||31/12/1990||CQF||Tim Morrissey||55 – 54||Liz Barber||Gyles Brandreth||Catherine Clarke||69|
|M93||7/01/1991-11/01/1991||M||Robert Violett||71 – 70||Liz Barber||none||Freda Thornton||134|
|1882||15/11/1996||eQF||Liz Barber||37 – 59||Richard Campbell||Barry Cryer||Susie Dent||76|
|3436||11/03/2003||LSF||Hilary Hopper||45 – 35||Liz Barber||Rick Wakeman||Alison Heard||85|