An alternative suggestion put forward by experts monitoring the regime in North Korea is that Ri Sol-ju may have crossed Kim Yo-jong, the leader's younger sister, who is increasingly emerging as the power behind her brother's throne.
Mrs Ri last took part in a public event with her husband on March 28, Yonhap News reported, when she accompanied Mr Kim on a visit to a new commercial district and health complex in Pyongyang.
Since initially appearing as North Korea's first lady in 2012, Mrs Ri was regularly seen alongside her husband as he carried out "on-the-spot guidance tours" of factories, hospitals and theme parks. She was pictured alongside him in state media on 22 occasions in 2013 and 15 times in 2014, but only three times in the first three months of this year and not at all since then.
"This is certainly something of a surprise as Mr Kim himself has been frequently pictured in the North Korean media," said Toshimitsu Shigemura, a professor at Tokyo's Waseda University and an authority on the North Korean leadership.
"There are several possible reasons, including that she is pregnant or that there is some sort of problem between the two of them," he told The Telegraph.
Mr Shigemura added that there are unsubstantiated suggestions that Mrs Ri was very close to Jang Song-thaek, the dictator's uncle and mentor, who was executed in December 2013 after being charged with a raft of crimes against the state, including "gnawing at the unity and cohesion of the party."
"There have also been reports of instability in Pyongyang and even of several attempted attacks, including by factions in the North Korean military, against Kim last year," Mr Shigemura added. "It is possible that Ri has not appeared in public because she is being closely guarded."
Another possibility is that Mrs Ri has in some way upset the dictator's sister, who was last year placed in charge of North Korea's propaganda and agitation department.
Her tasks include promoting her brother's cult of personality, while she also reportedly exercises a good deal of influence over Mr Kim.
"The belief is that while Mr Kim lacks political ability, she is far more adept at the sort of manoeuvring that is required to keep him in power, so that is the task she has taken on," Mr Shigemura said.
About Kim Jong-un
1983: Reportedly born in Pyongyang, though his true age is unknown
2011: Becomes Supreme Commander of the Korean People's Army after the death of his father, Kim Jong-ilApril
2013: Threatens US with "pre-emptive nuclear attack" on Los Angeles and Washington, D.CSeptember
2013: Disappears from public life for nearly a year, prompting speculation about ill health
December 2013: Reportedly executes his uncle after he is found guilty of treason
December 2014: North Korea denies claims it was behind cyber attack on Sony that delayed release of a film mocking Kim Jong-un
May 2015: Executes his defence chief with an anti-aircraft gun after he "fell asleep during a meeting," according to South Korean spies