First, there's Joan Blackman from Blue Hawaii:
Next, we have Anne Helm from Follow That Dream:
And here's Laurel Goodwin from Girls Girls Girls, with Elvis:
Next, here's Joan O'Brien from It Happened at the World's Fair:
Finally, here's Yvonne Craig from Kissin' Cousins:
If there's a pattern, I guess I'd have to say that someone was very consciously casting girls who were attractive in a wholesome way, but not so attractive that they would ever ever upstage Presley. Joan O'Brien I remember vaguely from another movie, Operation Petticoat, where she played Tony Curtis' love interest, and Yvonne Craig later went on to be Batgirl on Batman, but other than that, they've pretty much all receded into obscurity, their fifteen minutes of fame (and reflected fame at that, overshadowed by Elvis) up.