It was originally thought that Mark Bridger's appeal bid would be heard by leading judges at the Court of Appeal in London on January 24.
Bridger, a father of six, snatched April near her home in Machynlleth, Mid Wales, on 1st October 2012. Her body has never been found.
Sentencing Bridger in May, Mr Justice Griffith Williams said: "There is no doubt in my mind that you are a paedophile, who has for some time harboured sexual and morbid fantasies about young girls."
More top news
Accompanied by the Duke of Edinburgh, the Queen will attend the opening ceremony of the fifth session in the Holyrood chamber.
Ms Leadsom has received the backing of Ian Duncan Smith, the former work and pensions secretary.
The former shadow work and pensions secretary is considered a more viable candidate than Angela Eagle, a Labour source has told ITV News.