It's been announced that Sadie Miller (daughter of Elisabeth Sladen) will write a novel for Candy Jar Books, set within their Lethbridge-Stewart spin-off series. The book, titled Moon Blink, will be out in 2016.
There's more on the story at Doctor Who news - including quotes from the team at Candy Jar Books, as well as Sladen-Miller family friend (and SJA script editor) Gary Russell. It confirms that following Lis Sladen's death in 2011, Sadie turned her attention away from acting and towards the writing profession.
Well done Sadie - and good luck for future endeavours!