Nick Adams doesn't have that great of a reputation...he was a shady character. He knew talent when he saw it and he knew to stick with that talent and ride it for all the fame it could give him. He not only did this with Elvis but with Natalie Wood. Robert Wagner (Natalie's husband) told biographer Gavin Lambert that Nick was bisexual...The James Dean thing quite possible... And to give you more of an idea about how he was as a person, as Natalie began to see less and less of him/hang out with him (mid 60s) he started to threaten to reveal things about her to the press making her even more paranoid than she was at that time in her life. Robert had to block all contact between Nick and Natalie eventually because it got out of hand.
As for how much into the 60's they stayed in touch, there is a photo floating around of Nick on the set of "Follow That Dream" with Elvis. Nick also dropped in at the Colonel's 55th birthday party (June 26, 1964).
According to June Juanico (Elvis Girlfriend), Nick was paid by the Colonel to report back to him on Elvis...
Elvis was probably upset by Nick's death. But by that time I bet their friendship was something that was in the past...that they had just drifted apart.
Hope I said something that was helpful? As for the girl on the recording--I have no clue. I've heard the interviews with Nick, Vernon, and Gladys from that day...but as for anything else Maybe someday.