Question from Chapter 1 of Cornell, Silverman, Stevens "Modular Forms and Fermat's Last Theorem."

Question

On page 14 of the text, Stevens seems to imply that Lemma 7.8 is immediate from the result of Serre in the previous paragraph. However, I do not see why the residual mod $p$ representation attached to our elliptic curve $E$, denoted $\overline{\rho}_{E,p}$, must satisfy Stevens' Condition D (see page 12) that its restriction to $G(\mathbb Q(\sqrt{-3}))$ is absolutely irreducible. The result of Serre that the author quotes only applies when $p = 3$ by the author's own admission, but Lemma 7.8 merely requires that we deal with a prime $p$ at least 3. So what if $p$ is a prime larger than 3? How do we get Condition D?