We take our boys who are 8 and 11.
However, there are plenty of preschool-aged kids. You wouldn't be the only one there with a preschooler.
You might end up doing much of the hammering yourself, either that or you're going to have sore fingers from holding that little tiny nail while your kid whacks at it.

But I've seen plenty of Build and Grow where the Building was being done by adults, supervised by small children.
Our 8-year old is autistic. After a few months of me getting my fingers whacked repeatedly due to his total lack of hand-eye coordination, I now do the assembly while he instructs me.

That might be how it ends up with you too, but she'll think it's great fun. And a free apron and goggles, and a patch? It's very very cute. I think the December project is a wooden gingerbread house, it looks alot like the castle they did last year, it wasn't a difficult project.