However, he warned that the jury should not be prejudiced against her because of her Islamic clothing, saying she is 'fully entitled' to dress as she chooses.
The judge upheld a ruling that he made in September that the woman, who cannot be named for legal reasons, can wear a full-face veil during her trial as long as she removes it on the witness stand.
He told jurors today: 'Courts have known for many, many years, indeed centuries, that when a jury is evaluating evidence a witness gives it is important for them to see the witness as well as listening.
'In other words, you have to see the demeanour of the witness and reactions to the questions being asked.'
If the woman gives evidence, her identity will be verified by a female police officer and her face will be visible only to the judge, jury and lawyers.
Mr Murphy emphasised that jurors should not allow themselves to be influenced in any way by the defendant's choice of clothing.
'I am sure you will have noticed that the defendant is wearing a full face veil - it hides her face apart from a narrow slit for the eyes,' he said.
'Let me begin by saying that in this country everyone is entitled to express any religious view they wish, or to hold no religious view.
'Also we are entitled to express any religious view we may have in any way that we choose - that includes wearing a form of dress which a person may consider to be appropriate.'