Speaking of Priscilla as Elvis's ex-wife, I know that Elizabeth Taylor's son and Marlon Brando's sister were on Dallas, but were there any other relatives of big stars (and I don't mean the children of cast members) who were on the show?
As for Jenna as a character, she fulfilled her purpose, much like Mark. If the character had been too sympathetic, she could have damaged Bobby and Pam's status as the show's super couple. For me, Jenna is the only character on Dallas who overstayed her welcome, which is kind of sad. Perhaps the character's image among fans would be better today if Jenna had left the show before Bobby's death, maybe after the trial by realizing that Bobby loved Pam and starting a new life elsewhere.