Ze is verliefd op haar buurman. (She is in love with her neighbour.)
verliefd takes "op" (verliefd op = in love with). Example: Ze is verliefd op haar buurman. (She is in love with her neighbour.)
Ze is verliefd op haar buurman. — She is in love with her neighbour. The preposition op is fixed, so it doesn't change with the sentence.
Fixed prepositions come up all over the A2 exam. The platform drills them in real exam tasks, AI-graded across all five DUO sections.