Jules is mature and capable, a free-spirit, a spacey daydreamer, a bit of a tomboy, and an aspiring actress with pizzazz--the last according to a talent scout who overhears Jules' family at a cafe and asks her to audition for a commercial. Jules has many dimensions, which makes her an appealing character, perhaps the best being that she can draw attention to herself by being appealing rather than spoiled or bratty (unlike some of her literary peers). She has self-created problems, of course, worries and friendship issues, but nothing over-the-top and she has enough humility to see and admit when she is wrong.
In fact, for a book this short, all of the characters--her parents, brother, teacher, and peers among them--are pleasantly complex, realistic, and appealing. It makes for an enjoyable quick read that many different young readers will relate to.
My only quibble is that Jules seems a bit too mature, capable, and sophisticated for a seven-year-old; she seems more like she's nine or ten. And according to two different sources it is written at a fourth-grade reading level, a bit high for the target audience of a seven-year-old protagonist. It's not a huge issue, but something to be aware of.