While on the surface I agree, I can not help but think there may be more to it. Your lawyer may have been trying to make a point that by linking a comment made by a toxic public figure that the jury would have been swayed more in your direction.
As an example, let us say that your sister was charged with Crime X. And Adolph Hitler said that Crime X was a serious crime. Perhaps the attorney was hoping that the jury would go against Crime X since Hitler liked it?
That is why it is called law PRACTICE. Lawyers try different things, some work, some do not, and some work the first time and not the second. The lawyer may not have used his/her best judgment, but that is not to say that it was out-and-out wrong.
No one who is not close to the case can judge. What were the charges, the evidence and the entire closing? I would not quote Hitler on anything personally but your sister's lawyer may have had some plan of attack in mind. Why are you asking now 15 years later?