From the information you provided, it sounds as if they are investigating something else and needed an excuse to make contact. They may be watching her husband for something he may be involved in that she doesn't know about. There may also be a search warrant for their house coming in the future so she may want to check any computers in the house and go through them to see if there is anything that may shed light on what they could be investigating. In any event, they should NOT talk to any officers without an attorney present.
The police don't come to people's homes to have them sign admissions of guilt on traffic tickets. They have better things to do. If the police are casing your relative's house it is for some other reason. Follow my colleague's advice and do not speak to them.