From many, many years of study both independantly and under knowledgable men.
I would recommend you start with Road to Hel: A Study of the Conception of the Dead in Old Norse Literature if you want to understand the direction I come at the topic from.
Look at the start of the name, "HEL" is there.
Etymological Hel is the literal earth, i.e. where the dead are buried. The underworld from surface living dwellers. It roots to meanings like to cover or conceal (as dirt would cover the body).
To my thinking, all the various halls that play host to the dead are within Hel itself (Valhalla, Vingolf, Sessrumnir, etc.). So by extension Helgafell is merely a place within Hel in that context. If you haven't already, HREDavidson's Road to Hell is the best academic examination of Hel. That being said as an academic and not a believer her treatise is mainly hell is only a personification of the burial grave/earth, not so much a Goddess.
But if you look at the big picture we see in the stories of draugr, aptrgangr. haugbui, ketta... we see a concept of the living dead (and the importance I suspect in valueing the dead sothey don't plague you).
We know helgafell was a holy mountain, there were several such mountains that seemed to end up with this place name across Northern Europe. (And I echo the thought from u/HappyYetConfused that it was just a localized version of living folk religion/belief around death). One of the more famous is in Iceland. Eyrbyggja saga tells us there was a Temple to Thor built upon it. In the archaeological record we've found cairns on top of the mountain (and similar other mountains), and it looks like they were used to help determine time calendars based on how the sun hit it and cast it's shadows. It's also mentioned in Laxaela saga, as where Gudrun lived, and was later buried.
There's a paper written here with academic sources that looks into the bigger picture of the mountain and beliefs from Pagan to Christianity you may find interesting to read.