For some reason, even though we know better, authors make this kind of mistake all the time. In Domestic Violets, which I loved, the wife is named Anna, the stepmother Ashley, and the daughter Allie. Which all kind of run together.
The less forgivable mistake in the book I'm reading now is that pigeons are seen feasting on a dead body. Pigeons? Crows I would believe, but pigeons is just laughable. And yet there they are on about page 200, tearing at some poor fictional guy's entrails.