Interesting you should ask! Sandy’s accent has always been a bit of a special trait of hers because it doesn’t match any one region. Sandy started traveling at the age of 10 and over the years, her casual accent and mannerisms became a hodge-podge of the many places she’d been. It would take a truly skilled linguist to be able to determine the true root of her accent. To make matters more complicated, she tends to slip in an out of different accents subconsciously. Usually it’s to match the ponies around her but it also has emotional triggers as well. Anger tends to bring up a course, Manehattan accent, excitement can bring up her Appleloosan, and being informative often summons her Academic Canterlot. The ‘proper’ style of speaking tends to come up when she’s being analytical and it’s less an indication of her accent and more a glimpse into her thought process.
-TB