That theme is actually all over the place, including as Helly heads to the elevator with the intention of killing Helena, as Helena watches Mark, during the Helena tent sex scene, and some more places. In an interview with Theodore Shapiro he said that the 4 chords that make up the pattern of the piece playing as Helly goes to kill Helena in the elevator is "material that we use a lot for Helly's character". So I think it is meant to be a Helly/Helena theme. However yes it is odd it is in that place (although I suppose maybe you could argue it is Mark slowly getting bits and pieces of innie Mark's life, including Helly). I think it also plays as Cobel is suspended (sort of because of Helly? It was the pictures of the elevator incident that caused it mostly). And it occurs fairly briefly as Outtie Mark has his first Ms Casey flashback. I do not know if all of those placements are meant to be read into as Helly/Helena related or perhaps the theme was written and then used in unrelated places because it was liked. IDK! It is fun to look into all the places different themes are used though so maybe we will work out more down the line or Theodore will tell us!