Just for the sake of others who haven’t read the section you’re referring to, it’s on pages 278-281.
I went back and reread it, and for my discomfort over her use of the word “story” over “account”, I’m not seeing the contradiction of the Gospels or a rejection of the accounts. In fact, the historical blunder is on calling Judea, Palestine; a name the region wasn’t given until the 2nd. cen. in 132 BC/CE.
The Gospels don’t actually say explicitly what time of the year Jesus/Yeshua (which can be anglicized to Joshua; they didn’t call him Jesus back then) was born. The 25th of Dec.. was chosen later. One can deduce the time of His birth from the account in Luke; where he details the priestly duties. Knowing the order of the service of the Temple priests that had been established can bring you to a different date-the autumn, at the time of Sukkot (Feast of Tabernacles). However, being absolute and knowing the exact date doesn’t make or break my faith; but we history-buffs like to dig into the weeds of detail.
Plus, we truly don’t know the year of his birth, either. We have church traditions on these varying issues, but this is dealing with history, not faith or religious issues.
Also, the Gospels aren’t carbon copies of one another and there are differences.
Now, this may still be more than you want to present to your 8 year old, and you should do what you think is best; but I don’t think that makes the author “anti-Christian” or contradicting Scripture and I personally think it’s unfair to categorize her as such. She’s just challenging preconceived notions, assumptions, and/or religious traditions. She’s being an historian.
Each family should read it for themselves and make a decision.