Only Liars Shall Be Heard

A British woman, a victim of a robbery, seemed to be a very believable eyewitness. 

So the judge decided that she should NOT be allowed to testify. 

He put it like this:

Denise Dawson was a particularly impressive witness because she showed courage, clarity of thought and was undoubtedly honest. The jury may lend more weight to her evidence than her facts allow.

Was this woman 
just too good of a witness?

Or was the judge 
lacking in mental fitness?