The wife is the only witness to an assault and dose not wish to give evidence in court can she refuse to do so?

as she also knows the family of the accused and is intimidated by the threat of going to court.we recently moved out of the area,and she withdrew her statement.as she wanted no further involvement in the case,she has now been contacted by the police saying she is likely to be summond to appear at court.What can she do ? or dose she need legal advice from a Lawyer/Barrister.?