Patrique Kelly's young side had been eight points down at the interval against the defending champions, but Belton's first try gave them hope and her second sealed a remarkable season for the AIL newcomers.
The University of Limerick has served as a real rugby nursery for many of the current Shannon team over a number of years, but it has only been this season that UL Bohs has fielded a senior side in women's AIL One.
Bolstered by the signing of two student stars from Shannon in Belton and her fellow international Kelly, UL Bohs actually finished top of the league table in their first term as a top flight team.
They beat Shannon 6-5 when these sides met during the league proper earlier in the season, two penalties from the prolific Belton giving UL Bohs victory on that occasion and helping ensure that her former club had to settle for runners-up spot.
UL Bohs and Shannon had comfortable wins over Belfast club Cooke and Blackrock respectively in last month's play-off semi-finals to set up Saturday's decider, which certainly lived up to expectations.
Shannon, all of whose points came in the first half from Ireland A outhalf Denise Tracey, courtesy of a try and a penalty, seemed on course to retain the trophy they won in Thomond Park by beating Highfield 12-0 in January last year. But the 21-year old Belton, who scored a try and conversion that day in the blue and black jersey, had other ideas and her heroics ensured the Cup would be presented to another member of last season's winning Shannon side, UL Bohs captain and Ireland centre Kelly.
Clonakilty, captained by Munster flanker Eimear O'Sullivan, triumphed in the Division Two final, winning their all-Cork clash with Midleton 14-3 in spite of the skipper's teenage Ireland A colleague, winger Grace Sheehy, not being on the scoresheet for once.