Having only the vertex orbits (instead of the full automorphism group) is not enough to compute the edge orbits. Consider, for example, a graph of $n=6$ vertices where all vertices are in a single orbit (in other words, the graph is vertex-transitivevertex-transitive). From this information, you cannot differentiate whether your graph is
- $K_6$$K_6$, which is also edge-transitiveedge-transitive (all edges are in one orbit)
- the triangular prismtriangular prism, which is not edge-transitive
- or something else.