Let $\mathcal{A}$ be a ${{C}^{*}}$-algebra and $E$ be a Banach space with the Radon-Nikodym property. We prove that if $j$ is an embedding of $E$ into an injective Banach space then for every absolutely summing operator $T:\,\mathcal{A}\,\to \,E$, the composition $j\,\circ \,T$ factors through a diagonal operator from ${{l}^{2}}$ into ${{l}^{1}}$. In particular, $T$ factors through a Banach space with the Schur property. Similarly, we prove that for $2\,<\,p\,<\,\infty $, any absolutely summing operator from $\mathcal{A}$ into $E$ factors through a diagonal operator from ${{l}^{p}}$ into ${{l}^{2}}$.