Even though he wasn't charged with theft, has the accused admitted the theft, and that he bought the jewellery with the stolen money? If he has, then there really should be no problem in it being returned to your friend and the police should be willing to talk about it to her.
If he has not, then why have the police got the jewellery as it is presumably not evidence of anything other than theft?
Your friend is a victim of a crime and should have been put in touch by the police with a victim support service or suchlike. If she has, she should talk to that person and see if they can help get info out of the police.
If all else fails, there is a police complaints system. I think it normally starts with a letter to the Chief Constable.