I am certainly no fan of Wal-Mart, but I wasn't able to find anything on the internet on this story -- except dog-related cites that link back to Chloe's website. I couldn't find anything on CNN.com or abcnews.com.
I also searched for "pit-bull", "wal-mart", "service dog" and "chloe" on
abc7.com: Southern California's news leader (the news station chloe's owner claims interviewed her) and didn't come up with anything related to this story. Maybe someone else will have more luck.