Rolfö dribbled past a couple of defenders and got a distinct shot that went in at the right post unreachable for the goalkeeper.
The goal, in extra time in the first half, meant 3-0.
Jennifer Hermoso scored two goals in the match.
Barcelona is ready for the playoffs and in practice is also the second Arsenal, with Swedish coach Jonas Eidevall, it.
Third Hoffenheim is three points behind and with a much worse goal difference.