Interesting to note that Henry Lee Lucas's abusive father died of hypothermia as a result of collapsing outside drunk during a snowstorm when HLL was a teen. This is reaching, of course, but maybe the impending reports of a bad storm triggered something in him and he killed to commemorate the occasion. It doesn't fit any of the other known and accepted murders, but he did kill his 16 year-old "girlfriend" Becky Powell, so that age group isn't out of his range. There are so many unanswered questions about HLL that it's impossible to know. It was my understanding that in the late 70s, Lucas operated out of the Florida area, but your research proves I must have been mistaken!
I agree with you that it seems odd that a local girl at that time went missing and it was unsolved, just knowing what I do about our small state and its tightly knit communities, especially in the 1970s and especially in the Felton area. Im curious about the link to the horse racing community. I know that there was Brandywine Raceway up in the Wilmington area, and of course Delaware Park. Did Dover Downs offer horse races in 1979? Harrington? Anywhere on the Eastern Shore of MD? There wouldn't have been any horse races in February in our area, unless there is a now-defunct indoor track that I don't know of, but it's possible that she met someone or made a connection at one of those places. If she was indeed a runaway, she may have met someone who traveled the circuit that was able to give her transportation and a means to leave the state.
There are still many Kemps in the Felton area - I have to think that some of them are probably relations. I hope that they're able to find some closure to her disappearance in their lifetime.