maybe get her on her own with your mum to sit and talk explain that she is lucky the neighbour rang you and not police.let her know you are on her side.is it a possibility she is scared of saying anything to her partner?
but if she honestly doesnt think anything is wrong then you need to make the right decision on who else to contact...harsh i know but what if something really bad were to happen...god forbid.?
thinking of you at this hard time. xxx