The Guardian, which was my go-to election website (no paywall and it follows the AP reporting, which is why Biden has had the EVs from AZ all along), shows that Cascade County went for Covidiot 23,199 to 15,384 for Biden.

This graphic should show the vote total for the state. If not, just scroll over Montana and then click. For results in Great Falls, the county seat of Cascade County, you'll have to scroll over the counties.
https://www.theguardian.com/us-news/ng-interactive/2020/nov/07/us-election-2020-live-results-donald-trump-joe-biden-presidential-votes-pennsylvania-georgia-arizona-nevada

Your granddaughter most likely voted as an absentee from OR. But if she voted as a Montanan, she is one of the 15,384.

As an aside, the other strongly blue areas in the state are Silver Bow County (Butte), Deer Lodge County (Anaconda) and Gallatin County (Bozeman); Glacier County, Blaine County and Big Horn County ALL have a strongly Native American voting presence.

Butte and Anaconda have still remained Democratic strongholds and Montana Tech is in Butte. Bozeman has the Montana State University-Bozeman.

Lewis and Clark County (Helena), while Red, has one of the closer vote margins in the state. It is actually more Purple than Red.

Great Falls was, for a very long time, strongly Democratic, largely because of the Anaconda Company smelter and refinery in Black Eagle, which had a unionized work force.

Anaconda's departure 40 years ago, after it merged with Atlantic Richfield, was a huge loss to the state's extractive economy. Nothing since has really made up for that. Ever since, the state has gotten redder, most recently being flooded by wealthy "immigrants" from other states, one of whom is Greg Gianforte, aka "Giant Fart," who dumped in $7 million+ of his own money to buy the Governor's seat.

This is an old article, but a good one, about the Anaconda Co. departure. https://mtstandard.com/news/local/anaconda-smelter-30-years-later/article_1177866e-c92d-11df-8251-001cc4c002e0.html

For other information, see Marcus Daly: https://en.wikipedia.org/wiki/Marcus_Daly

If you're interested, here's some good reading about the impact of copper mining on Montana's history and development. https://www.amazon.com/War-Copper-Kings-Greed-Politics/dp/1931832218