I don't think there is any. It sounds like the father was involved in his son's life to a point, but I don't think that there was a continuing relationship with mother. I'm imagine LE has cleared him already.
I really don't see the father being involved with the death. I know in most cases, the first person looked at is the spouse/boyfriend/childs father, but in this case, I don't think so. JMO.
To add another opinion: Her part time job was in a restaurant. These small towns sometimes only have one restaurant, and many have regulars. Was there a customer who repeatedly searched her out to be their waitress? Was she stalked by a regular customer? Often times, waitresses flirt harmlessly with patrons in order to get a better tip. Was there one who took her flirting seriously?