South Korea's National Intelligence Service (NIS) had told politicians Ms Ri appeared to have steered clear of outside activities to prevent coronavirus infections, but she was "playing well with their kids".
A man from North Korea has crossed the heavily fortified DMZ into South Korea.
It is the first official confirmation that the North has asked for worldwide help, with the country's medical infrastructure seen as woefully inadequate for dealing with any large-scale outbreak.
North Korea had requested Covid-19 vaccines earlier this month and was expected to receive almost two million doses, according to the Gavi vaccine alliance, part of the WHO-backed Covax program.
Although the NIS did not say when the alleged hack took place, or whether it was successful, it is at least the second North Korean effort to steal vaccine data. Pfizer's coronavirus vaccine, developed jointly with Germany's BioNTech, began winning approval from authorities late a year ago.
Ri Sol Ju's appearance comes the same day South Korea 's intelligence service sought to play down rumours over her "disappearance". The coronavirus vaccine jointly developed by Pfizer and German biotech firm BioNTech is one of the few that has been approved for emergency use by the World Health Organization. Financial institutions and exchanges were hacked to generate revenue for Pyongyang's nuclear and missile development, the document said, with the vast majority of the proceeds coming from two thefts late past year.
Park was also accused of involvement in an $81 million heist on the Bangladesh central bank and a 2014 cyberattack on Sony Pictures Entertainment in apparent revenge for its movie "The Interview" - a spoof about an assassination attempt on the North Korean leader. The attack resulted in the posting of several unreleased movies as well as a vast trove of confidential documents online. Pyongyang's hackers were blamed for the 2017 WannaCry global ransomware cyberattack, which infected some 300,000 computers in 150 nations, encrypting user files and demanding hundreds of dollars from their owners for the keys to get them back.
Cross-border ties soured after denuclearisation talks between Pyongyang and Washington stalled in 2019.