Royal icing not going into stiff peaks

[Sonea]

Have followed Delia's instructions faithfully but can't get my icing to rise into stiff peaks, do I need to add more icing sugar or another egg white?

More icing sugar.
Did you add the sugar really slowly? And lightly beat the egg first?

I added the icing sugar spoonful at a time but didn't lightly beat egg first as she didn't tell me to do that.