Bloomberg has an article published that looks at the importance of the wife and sister of Kim Jong-un:
One sports a Christian Dior handbag and favors Western clothes. The other carries a notebook and wears dark uniforms. These fashion opposites are the two most influential women in North Korea.
While Kim Jong Un’s wife Ri Sol Ju and younger sister Kim Yo Jong are currently allies in sustaining one of the world’s most reclusive leaders, their overlapping influence makes them potential rivals in a regime where family ties aren’t strong enough to protect against Kim’s penchant for purges.
These women of Pyongyang offer insight to an opaque regime that, while struggling to feed its people, is capable of maintaining 1.2 million men under arms and threatening neighbors with nuclear annihilation. Ri commands a growing following among the wives of North Korean elite while Kim Yo Jong now holds a senior position in the ruling Workers’ Party and serves as an adviser to her brother.
“Uneasiness is inevitable in a relationship like this,” Kang Myong Do, a son-in-law of North Korea’s former Prime Minister, Kang Song San, said by phone. “The wife wouldn’t like it if her husband got too close to his sister; the sister wouldn’t like it if her brother got too close to his wife.”
The sister would try to oust Ri if the first lady_ a “rag-tag commoner” compared to Kim Yo Jong — sought political power beyond the role of burnishing her husband’s public image, said Kang, who now teaches North Korean studies at Kyungmin University near Seoul.
Kim Yo Jong chooses to remain in her brother’s shadow at public events, while Ri locks arms with Kim Jong Un. In a photo released Jan. 21 by the state-run Rodong Sinmun newspaper, Kim Yo Jong hides behind a pole as she watches the back of her brother speaking to people at a shoe factory.
Still, Kim Yo Jong “has a lot of control over who has access to her brother, what they say to him, what documents they hand over — in short, she is a combination gatekeeper and traffic cop,” said Michael Madden, editor of the North Korea Leadership Watch blog. [Bloomberg]
You can read more at the link, but for all we know Ri Sol-ju and Kim Yo-jong could be best friends and thus no potential of power struggle between the two. I think it is pretty clear that Ri Sol-ju is there soften Kim’s public image while Kim Yo-jong is a person he trusts who takes care of things behind the scenes.