Let N be a compact, connected, non-orientable surface of genus ρ with n boundary components, with ρ≥5 and n≥0, and let M(N) be the mapping class group of N. We show that, if G is a finite index subgroup of M(N) and φ:G→M(N) is an injective homomorphism, then there exists f0∈M(N) such that φ(g)=f0gf−10 for all g∈G. We deduce that the abstract commensurator of M(N) coincides with M(N).