Artist's description from DA:From the farm to the battlefield, Applejack definitely saw the least Basic training of the Mane Six. Doesn't mena she saw the most battle, it just means she knew to take orders and memorized what needed memorizing fast enough that she could be boated off with her infantry regiment ASAP. She wasn't tall enough to be admitted into the Juggernaut division of the Army but she was still used for her brute strength. Her armor was thick and her bravery was unwavering. Unfortunately her comrades in arms did not have such luck. Some were captured, many others were injured or killed. The lack of constant officers on the field led AJ to take control of what was left her regiment and lead them to safety. They eventually found themselves in Liongrad, Gryphus and joined other Equestrian forces in a huge attack. Applejack was present at the successful Seige of Liongrad.
After the battling was over, it was back to the farm. She returned to Applebloom, Big Mac, and Granny Smith. A few years later, after she was married and when her first baby was on the way, Granny handed Sweet Apple Acres over to her and her husband. Big Mac was preoccupied with his own family start up and had decided to move off the farm. Applebloom was still under custody of Granny.