Born on April 14th, 2158, Ashley Madeline Williams comes from a large family that includes a long line of Alliance soldiers. Her father was an enlisted man and she is the oldest of four daughters in the family, followed by Abby, Lynn, and Sarah. Due to her father's frequent deployments, she helped to raise her sisters, and the four siblings grew close to one another as a result. Despite his hard work and dedication, Ashley's father never rose above the rank of Serviceman third class, a fact she is deeply bitter about.
Source: Mass Effect Wikia, "Ashley Williams," available under the CC-BY-SA License.