In Summer's younger days, she enrolled in Beacon Academy and became a member and the leader of Team STRQ, along with Taiyang Xiao Long, Raven Branwen and Qrow Branwen. She and her team eventually graduated to become Huntsmen and Huntresses.
At some point later in life, Summer entered a relationship with Taiyang after Raven had left him, the two having a daughter, Ruby Rose, and Summer took to raising Raven's daughter, Yang Xiao Long, as well. According to Yang herself, Summer loved Yang as much as her own daughter Ruby, and never corrected Yang's assumption that Summer was her biological mother; it wasn't until after Summer's death, that Yang learned she was Raven's child, rather than Summer's. Summer's family lived in Patch as she left regularly to carry out missions. According to Yang, Summer was like a "supermom", "baker of cookies" at home and "slayer of giant monsters" due to her Huntress career.
It is revealed by Qrow that Summer acknowledged and utilized her abilities through her Silver Eyes. It is unknown when and how she discovered her abilities and to what extent.
At some point, Summer encountered Salem, where she told her that she'd be stopped even if she could not be killed. This encounter was memorable enough for Salem to remember her words.
When Yang and Ruby were still young, Summer went on a mission and never came back. Specific details surrounding her fate are undisclosed or unknown. According to Qrow, the mission in question was Summer's secret and even Ozpin seemed in the dark about her disappearance. According to Yang, Ruby was likely too young to be able to fully comprehend what had happened, though both she and Yang were grief-stricken.
Taiyang did not handle the news nearly as well as his daughters; Yang saying that he simply "shut down". It is after this that Yang learned Summer was the second love that he had lost, the first being Yang's mother, explaining that Taiyang was so deeply affected due to the fact that he had to experience that type of loss for the second time.
It is implied in "Gravity" that Salem is responsible for Summer's death.
In "The More the Merrier" Ruby attempts to sway Raven into joining the fight against Salem. Raven responds, somewhat contemptuously, "You sound just like your mother", before beginning the attack on Haven.
In "Pomp and Circumstance", Ruby and Qrow have a conversation about Summer's last mission and the unknown nature of her disappearance. Ruby also wonders what she would've done had she learned the truth about Salem, to which Qrow tells her he believes she would've pressed on, like her.
During "Gravity", Ruby tells Salem that even if killing her is impossible, she can still be stopped. However, Salem looks at the girl and tells her that's exactly what Summer said, and that in the end it wasn't true. Ruby proceeds to break down in grief, thinking of her mother.
In "Witch", Yang calls Salem out on all the destruction she's caused and that everyone she's lost was because of her. When Salem scornfully asks who she's taken from Yang, the latter replies Summer, which causes Salem to smile at hearing her name again.
In "Risk", having killed The Hound only to discover that its' core was a Silver-Eyed Faunus, Ruby wonders if Summer met the same fate. Filled with horror and despair, she theorizes to Yang that Salem stopped killing the Silver-Eyed Warriors when she encountered Summer, because she found a new use for them. Despite being devastated by this possibility, Yang affirms that Summer took a risk when she left for her final mission, and that, regardless of how it turned out, she was still her hero.