The Rise of Skywalker novelization reveals that Leia Organa did some of her training with Yoda and Obi-Wan Kenobi. Leia's connection to the Force has been one of the more controversial elements of the sequel trilogy, though the seeds were planted in the original trilogy decades ago. Rian Johnson famously gave fans "Leia Poppins" in The Last Jedi and J.J. Abrams delivered a young Luke and Leia training before she got pregnant with Ben Solo. Star Wars fans have debated this element of the storyline for quite a while now.
While some Star Wars fans may have taken issue with Leia's Jedi training, The Rise of Skywalker novelization attempts to justify it. As it turns out, she was more powerful in the ways of the Force than a lot of people knew. Leia was even able to tap into the Force directly to receive help in her training, which she later gave up to be a mother. You can read an excerpt from the novel below.
"Leia was no Jedi Master, but she had learned from the best. And not just from Luke; over the years she'd occasionally heard the voice of Obi-Wan Kenobi through the Force, and even more rarely, that of Yoda. Some days it had felt as though she'd learned from the Force itself."
The powers of the Force expanded greatly in the sequel trilogy. A lot of fans wanted to see Leia tear down some enemies with a Lightsaber, which unfortunately didn't happen. However, we were all teased with what could have been in The Rise of Skywalker with her training session. Plus, Carrie Fisher's daughter, Billie Lourd, was able to suit up as the younger version of the character for the training scene in the movie, which is a nice tribute.
Leia was a big part of The Rise of Skywalker, thanks to some unused (and reused) footage of the late Carrie Fisher. The plan all along had been to make the final installment in the Skywalker Saga have Leia as one of the main focal points, so J.J. Abrams and Lucasfilm did the best that they could to make that happen one last time. In the end, they were successful with using the older footage and repurposing it for the new narrative.
In the end, The Rise of Skywalker was always going to focus on Rey and Kylo Ren. Both characters had been developed throughout the trilogy and there was still a lot of story to tell. Star Wars fans were shocked to learn that Rey is Emperor Palpatine's granddaughter, though Leia and Luke seemed to have known the whole time. Regardless, it was still a shock for everybody. For fans looking to get a more comprehensive overview of what happened in The Rise of Skywalker, the official novelization sounds like a great place to start. You can head over to Penguin Random House to get your own copy of the book.