What the heck are the lyrics of this folk song talking about?

On an LL Bean ad I heard the first part of this old folk song "“I Found Her Little Footprints in the Snow” ".

and it sounded so merryI decided to google it up, but the rest of it isn’t so merry. “Bless that happy day when Nellie lost her way” seems an odd sentiment for a person freezing to death. What’s “merry” about it.

Here’s a link to the ad. From this page of the Mt Washington Observatory.

You seem to have answered your own question.

I’m assuming she died of exposure. Do you have a different take on it?