From Applejack to Rainbow Dash:  
Applejack - 120 cm. (~4 feet) AJ is one of the tallest, if not the tallest mare in Equestria, she is taller than most stallions in the country. In my AU the Apple family has really tall genetics, almost all of the relatives are abnormally tall, AJ happens to be the tallest mare in the Apple family tree.
 
Pinky Pie - 115 cm. (3’8 feet) Pinky, is the tallest of the four Pie sisters, in the show she is super energetic and talks  
fast, so a tall slim-like body is what I think would suit her.
 
P. Twilight Sparkle - 1 m. (3’5 feet) Twilight has grown taller since her alicorn ascension, she also got a bit more muscular - it’s because her body needed to get stronger to adapt to the huge boost in magic added to her
 
Fluttershy - 97 cm. (3’2 feet) Fluttershy is the average mare hight of Equestria, so nothing that special about her (still got that heart of gold though).
 
Rarity - 91 cm. (3 feet) Rarity, unlike most unicorns, has the body of a pure unicorn - lion tail, hooves in the color of her eyes. (A Pure Unicorn in my AU has more potential for magic capability than a regular unicorn).
 
Rainbow Dash 85 cm. (2’8 feet) Rainbow Dash, one of the shortest mares in Equestria, but very muscular ( I mean… She’s a Wonder Bolt, she should be at least a bit athletic), though despite her size she has shown a lot of ponies and creatures that she can do as good as them. I just recently started liking the idea of Dash being the shortest of the group, just makes her work harder to achieve her goals.