Her opponent was supervising the registration of voters and collection of votes in his own election as the sitting Secretary of State, he refused to resign, and he famously purged thousands of voters, mostly African American.
And, in addition to that, she's just a much more qualified person anyways. She has a law degree from the best law school in the country, a master's in public policy from the LBJ School of Public Affairs at UT, was a Truman Scholar, and worked in government at the state, federal, and municipal levels. Kemp has a BA in agriculture from University of Georgia. He was a state senator for two years, lost his run for ag commissioner, and was then appointed to his Secretary of State position. He's a fucking can and he's corrupt POS to boot.
It's understandable why she's sour and not keen on accepting her loss as valid.