During the first season, Kenna is arguably the most notable of Mary's close friends. While she is a Lady for Mary, she ends up being in a unofficial relationship with Mary's soon-to-be father-in-law King Henry II of France. Kenna really likes the king but when he starts to go mad, they have a falling out.
And strangely King Henry II decides to marry her to his bastard son Bash in a bizarre bout of mental illness. While they could have probably gotten the Catholic Church to annul the marriage, they strangely stay married after Henry's death.
And Bash and her eventually start to love and care for one another. But she wants Bash to be elevated to a baron or a duke. Bash doesn't want to, he wants to be close to his King and Queen at all times which he could not do as a nobleman.
Eventually King Antoine of Navarre tries to win her over. While Kenna is very beautiful, he was really doing it to get revenge on Bash, as he believed he murdered his brother during a previous war. This eventually causes Kenna and Bash to call their marriage off.
And near the end of her story in the series, she is trying to find a new groom to marry and she is always stumbling short.
The show kind of assumes she went to live near Sweden or Russia after leaving France. She wasn't one of my favorite characters in the show, but I liked her.