Lee turned pro at the end of 2019 and went to LPGA qualifying school, where she finished tied for 30th to earn a tour card for 2020.

In 2020, the whole world was rocked by the Covid-19 pandemic. The LPGA and KLPGA tours canceled and postponed many tournaments. Lee started her LPGA career with two events in Australia. She did not play again until the Drive On Championship at the end of July. But it was the next event that was her breakthrough: she finished tied for 5th at the Marathon Classic, her first career top five.

She followed that up with an 11th at the Scottish Open and a tie for 7th at the Women's British Open, her first career top ten in a Major. Lee cooled off considerably after that, finishing no higher than t-20th the rest of the year. Unfortunately, she was diagnosed with Covid and forced to drop out of the US Women's Open in December, but she was in the field again the following week.

In all, Lee had a very solid first year on tour: she made nearly $243,000, which put her 48th on the money list. She struggled more in 2021, however. She made just $107,000 that year, which was just 109th on the money list. As a result, she fell to category 15 for the 2022 season. Her best finish was a T-14th. She missed 10 cuts in 18 starts.

2022 was the breakout season for Andrea. She had her first win, destroyed her best season scoring average by more than 2 strokes, and made more than four times as much money in 2022 as she had in any other season.

Lee's win came in Portland in September. She shot her career best score, a 64, in round 2, and followed that with a 67 and 66 to just beat several other players, including rookie Na Rin An. She came close to a second win in Korea the following month, but soon-to-be world #1 Lydia Ko was just too strong and Lee finished 2nd. She had two tie-4ths, a 5th and one other top ten and made over a million dollars for the season. This earned her category 1 status on tour for the first time in her career.

Lee had a far less impressive 2023 season. She earned a little less than $600,000, which placed her 48th on the money list. Her best finishes were a pair of ties for 9th at the Scottish and British Opens. She also played in the Solheim Cup for the first time, where her record was 1-2-1.