Melanie Smith will be sentenced on 8 May for murdering five members of the same family in a flat fire in Prestatyn.
Mr Justice Griffith-Williams warned the 43-year-old that she should expect a life sentence.
More top news
Leaders of Wales, Scotland and Northern Ireland meet in Downing Street for talks with Theresa May ahead of Britain's departure from the EU
The prime minister has offered Scotland, Wales and Northern Ireland a "direct line" to Brexit Secretary David Davis.
22-year-old Ify Iwobi has been making music since the age of seven.