Symbolism, Imagery, Allegory
Villa Villekulla is "way out at the end" (1.1) of the town, much in the same way that Pippi, and her behavior, are way out at the end of the continuum of what's proper and acceptable—so yeah, the house is a reflection of (and a symbol for) Pippi.
Additionally, her garden is wild—much like Pippi—but still "really lovely" (5.24). Again, much like Pippi. Lindgren goes on to say:
You couldn't really say it was well kept, but there were wonderful grass plots that were never cut, and old rosebushes that were full of white and yellow and pink roses—perhaps not such fine roses, but oh, how sweet they smelled. (5.35)
Notice the similarities there? Pippi's not exactly the most put together when it comes to her appearance, but like the roses, she's got the qualities that matter.
Finally, we hear that in addition to plenty of fruit trees, Pippi's garden has "several ancient oaks and elms that were excellent for climbing," whereas "the trees in Tommy's and Annika's garden were not very good for climbing" (5.35). You can bet the Settergrens' garden and home are very well-kept, but just as "the people in the little town loved to go walking out Villa Villekulla way, for the country out there was so beautiful" (5.2), Annika and Tommy seem to prefer the wilderness of Pippi's environs to their own, more manicured, homestead.