Arrighetti's try, four minutes from time, saw Italy complete a dramatic comeback and seize a 12-11 victory in Wales, having been outclassed by their hosts in the first half.
Wales began in dominant fashion, pinning Italy back into their own half for large periods and they will rue not having more than a Lowri Harries try and a Robyn Wilkins penalty to show for their efforts.
Italy came out for the second half a far different proposition as their bigger pack rumbled into gear and the Welsh defence was finally breached in the 61st minute.
Hooker Melissa Bettoni crashed her way over after a sustained period of pressure and Michela Sillari's excellent conversion put Italy just one point behind and suddenly their self-belief was visible.
Wales edged further ahead when debutant Wilkins kicked a penalty in the 64th minute but with Italy's juggernaut pack being urged forward by scrum-half Sara Barattin at every opportunity, Wales' defence was being forced to work overtime.
Eventually Italy managed to work their way towards the corner flag and with four minutes remaining flanker Arrighetti delivered the killer blow when she powered her way over from close range.
Wales rallied in the dying minutes but the driving rain made handling a lottery and when Sioned Harries spilled the ball forward, Italy gleefully took the honours.
