We are all imperfect due to the fall. We are all corruptible–only God is incorruptible. For this He united His nature with ours, so that we might unite ours with His–thus various saints have said, “God became man so that man might become God.” We partake of the divine nature through our union with Jesus Christ, true God and true man.
This can only take place in union with His Mystical Body, which is the Catholic Church. This is why the Church even recently has affirmed that those outside her are objectively in an “gravely deficient” situation (Dominus Iesus, 22).
Since apart from the Body of Christ, which receives salvation through its Divine Head, there is no remission of sins, that perfection cannot be achieved elsewhere.
The problem with what Coulter said is she seems to be operating from evangelical or fundamentalist errors by which she sees the “perfection” as happening at the moment of conversion. Whereas, the truth is that Baptism, by which we become members of the Body of Christ, is the only the beginning of the process of perfection.
Members of the Body of Christ therefore have the potential to be perfected whereas those separated from the Body of Christ do not.
So while it is true that Jews need to be perfected, so does everybody else this side of Heaven. The difference is those who remain separated from Jesus Christ, who do not unite themselves to Him and cannot partake of the divine nature, cannot be perfected.