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Just 10 days before her high school graduation, 18-year-old Lucy Westlake became the youngest American woman to reach the top of Mt. Everest.

The Naperville, Illinois teen reached Everest's top — roughly 29,032 feet — on May 12 at 5:30 a.m. according to an Instagram post Friday morning, after an expedition that took 26 days.

"Looking up at the summit from camp 4 the day before our summit push, it truly looked impossible, but that night at 9 p.m. we began our climb and 8.5 hour later we did it!!," she wrote in a caption on Instagram along with a series of photos documenting the impressive feat.

Westlake is currently working to complete the "Explorers Grand Slam" — a challenge that includes summiting the seven highest mountains of every continent (Everest, Aconcagua, Denali, Kilimanjaro, Elbrus, Vinson Massif, and Puncak Jaya and Kosciuszko) and visiting the North and South poles.

She's been documenting her adventures on lucyclimbs.com. In 2017, Westlake climbed Mt. Kilimanjaro, followed by Mt. Elbrus in 2019 and Denali in June of last year. In January, she reached the top of Aconcagua, also known as the "Mountain of Death.

After Everest, she has just four to go to complete the grand slam: Puncak Jaya (a.k.a.) Carstensz Pyramid, Vinson Massif and both Poles.

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Breaking records isn't new to Westlake. Last year, at the age of 17 became the youngest woman to reach the highest points in all 50 states. In 2016, at the age of 12, she became the youngest female to climb the lower 48 state highpoints.

In her celebratory Instagram post, the teen also shared photos of some of the views from her climb and images of some of the people who helped get her to the top, including her sherpa, Mingma.

"Big shout out to Mingma, the absolute greatest sherpa in the world who has now climbed Everest 16 times (he's crazy) and Extreme Climbers for backing me up the whole way (love you Pemba)," she continued in her Instagram caption. "And of course, my biggest sponsors/emotional supporters: my family💕 Thank you all for believing in all my insane dreams."

On Thursday, Westlake's mother shared the news from the teen's Instagram account that she had reached the top writing. "💥AMERICAN RECORD 💥 Lucy stood on top of the world at 5:40 a.m. (Nepal time) making her the youngest American woman to summit Everest."

Westlake, who is now making her way down the mountain, did not immediately respond to PEOPLE's request for comment but she did call into the Today show on Friday morning from Lukla, Nepal.

"It was absolutely incredible," she told Savannah Guthrie and Hoda Kotb, recounting her trip to Everest. "Being at the top, I couldn't imagine that I was at the top of the world. I looked down and there was nothing higher."

She said though she thought she would cry once she reached the summit, her tears came earlier in the day as she watched the sunrise and realized she was so close to the top.

Westlake have been climbing since she was just 7 years old. She's usually joined by her father on climbs, though this time she conquered it on her own.

"One of the hardest parts, maybe the hardest part for me, was not having my dad there, just being completely alone," she said. "I love my sherpa, he was amazing, he was like my stand-in dad but it's not the same. It was really tough being away from everyone, anyone I knew for 26 days."

Westlake said while her parents were nervous about the trip, she explained they have a lot of trust in her — admitting her mother was probably more nervous about the smaller mountains she climbed as a child than Everest.

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Asked what motivates her, Westlake said it's all about finding that inner strength.

"As the mountains grew and it got harder I really had to find that deeper motivation to still want to do them and it's really just pushing my limits," she said. "I just want to see how far my body and mind can go and I hope to inspire others to do the same. That's how you figure out who you are...just by seeing how far your body and mind can go."

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Climbing isn't just about breaking records, either. Part of her missions is to show younger people and women that they can get into the industry. She also hopes to raise awareness and money about the world water crisis.

Her other big mission? College. After graduating high school early with a 4.6 G.P.A., Westlake is heading to the University of Southern California this fall, where she will run on the track and field team — another passion for the young adventurer.

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In the months leading up to her Everest climb, Westlake set up a GoFundMe to help raise funds for the trip.

Of the $40,000 goal, Westlake raised $23,810 as of Friday morning. On the page, she explained that she dedicated this climb to the AWE Summit Scholarship Foundation — an organization that helps "break down barriers of entry to the big mountain realm for women from all walks of life."

"Mountaineering is a sport dominated by men twice my age and size who can shoulder 75 pounds of gear with ease," she wrote. "And I'm ready to fight to change that. To show this generation of young girls that we belong in the mountains."

On the page, Westlake wrote that she graduated from high school early and is fogoeing prom and her graduation ceremony to "pursue something far greater than myself."