Because of Winn-Dixie. The title pretty sums up Opal's summer. Because of that friendly mutt Winn-Dixie, Opal
The cool thing about this title is that the "because" tells us that Opal gets it. She's smart enough to see how all these events interact, so this isn't just a story about how she got a dog last summer and he got up to some crazy antics. Nope, she understands that when Winn-Dixie came into her life, things got a lot better.
Here's something else: the title isn't quite right. Who knew right away that Winn-Dixie was just misunderstood? Who stood up for him in the middle of the grocery store? Who stood up to her father and brought the mangy, dirty dog home?
Opal. So we have to ask: should the book really be called Because of Opal Buloni?