Dottin, at only age 21, is the first West Indian to reach the milestone of 50 T20Is.
South Africa, winning the toss and batting, struggled to 113 for seven from their 20 overs with captain Mignon du Preez top-scoring with 39 not out and Cri-zelda Brits getting 36.
The Windies attack was led by left-arm seamer Shanel Daley (2-14), leg-spinner Shaquana Quintyne (2-18) and off-spinner Stafanie Taylor (2-24) all of whom picked up two wickets apiece.
In reply, Barbados batted in partnerships and overcame a stoppage for rain late in their innings before closing out convincingly.
Kycia Knight and Stafanie Taylor put on a run-a-ball 23 for the first wicket, to give the hosts a sound start.
The left-handed Knight stroked an unbeaten 33, anchoring the innings with a patient knock that consumed 46 balls and included three boundaries.
Taylor, meanwhile, scored 13 from as many balls before cutting 18-year-old left-arm seamer Chloe Tryon to Brits at point in the fourth over.
Shemaine Campbelle joined Knight and batted sensibly, added a further 23 for the second wicket in a quiet knock of 14 from 22 balls.
In a rare attacking moment, Campbelle advanced down the track to experienced off-spinner Sunette Loubser, missed her stroke and was stumped.
There was to be no comeback for South Africa, however, as Dottin combined with Knight to bat the visitors out of the game.
Dottin stroked three fours and three sixes as she dominated the unbroken third-wicket stand of 68, playing positively against the varied Proteas attack.
SOUTH AFRICA innings
S. Fritz c Mohammed b Quintyne 17
S. Cordes run-out 0
M. du Preez c wkp. Aguilleira b Taylor 39
M. Kapp stp. Aguilleira b Quintyne 4
C. Brits c Quintyne b Taylor 36
D. van Niekerk c Nero b Daley 10
S. Benade c Mohammed b Daley 1
C. Tryon not out 1
E. Theunissen not out 0
Extras: (lb-2, w-2, nb-1) 5
Total: (7 wkts, 20 overs) 113
Fall of wickets: 1-14 (Cordes), 2-24 (Fritz), 3-38 (Kapp), 4-95 (Brits), 5-110 (du Preez), 6-112 (van Niekerk), 7-112 (Benade).
Bowling: Selman 1-0-12-0 (nb-1), Daley 4-0-14-2, Taylor 4-0-24-2 (w-1), Quintyne 4-0-18-2, Campbelle 3-0-19-0, Mohammed 4-0-24-0.
WEST INDIES innings
K. Knight not out 33
S. Taylor c Fritz b Tryon 13
S. Campbelle stp. Cordes b Loubser 14
D. Dottin not out 48
Extras: (b-1, w-4, nb-1) 6
Total: (2 wkts, 18.2 overs) 114
Fall of wickets: 1-23 (Taylor), 2-46 (Campbelle).
Bowling: Kapp 3.2-0-12-0, Benade 3-0-28-0 (w-2), Tryon 3-0-20-1 (w-2), Letsoalo 4-0-21-0 (nb-1), Loubser 3-0-19-1, van Niekerk 2-0-13-0.