Sarah, being a muggle-born, grew up...as a muggle. She had an easy time of it, all A's in school, three great friends, loving parents, an awesome martial arts sensei. Her magic showed up, in the forun of some pretty impressive fireworks, when she was seven. A few years later, she was off to Salem Witches' Institute.
Whilst at school, Sarah excelled in charms and DADA. She loved potions, even though her grades in that class didn't pull up until her sixth year. She graduated saludatorian, with two amazing best friends, one of whom went on to teach DADA at Salem fifteen years later.
When she got out of Salem, she was recruited by the CIA and went straight into her special division. She was in training for two years and went on her first mission when she was 19. It was a fairly simple mission, just grabbing an agent out of a cellar, but Sarah herself got captured by a man named Michael (last name unknown.) He let her go after a few days, having not even touched her. they'd basically chatted the whole time, and, by some weird happening, exchanged numbers. A few weeks later they met up and dated for a while and, well... had a beautiful daughter named Nik. Soon after, Michael had to leave; his situation had become too dangerous for him to stick around.
And so Sarah raised Nik by herself, only slightly sad that Michael was gone. But her little devil was a wonderful blessing and made it all worthwhile. Michael was killed when Nik was eleven (aka when Sarah was 30), and that sent Sarah into a brief alcohol spree...but she got out of it for a while.
After a few years, she got her letter from Salem and she was, of course, overjoyed, as was her mother.
When Nik had to leave Salem, Sarah got a flat in London and started setting it up, deciding it was about time for her to leave the CIA. When Nik left for Hogwarts, Sarah went back to the States, not quite ready to retire yet.
But in September of Nik's sixth year of school, at 36, she had to leave all that behind for a longer-term mission. One of the top operatives was missing, and it was Sarah's job to get her back. She did...at a price. Sarah ended up having to stay behind to get her rescue out, and came very close to dying in the process. She was trapped, imprisoned, for almost all of September and all of November, December, January, February, and March, being constantly questioned, starved, tortured, etc. She got out, though, safely, and made it back to England, but waited to reveal herself, since it was still a bit too rocky for anyone to know she was alive quite yet...which tore her apart because she knew her daughter believed she was dead.
Sarah retired from the CIA as soon as she she could finalize everything that was necessary and went to work for the Auror office in London.
Sarah also has issues with alcohol. She can handle her alcohol well, but when she really lets loose and just drinks, it becomes a problem. She never really had a problem with liquor until Nik's dad, Michael, died. She began to be...perpetually inebriated to some extent. Sometimes she needed several shots just to get up and go into work. No one really thought anything of the small changes in her personality; the thought that Sarah Grey would ever abuse her drink was just so foreign...It was several months before anyone put a stop to it, and of all people it was poor eleven-year-old Nik. Sarah is a fickle woman when drunk. She can swing from complete depression to utter joy at the drop of a hat...or she can conceal her state by just keeping her mouth shut--as much as she can, anyway.
Sarah was sober for six years before she started self-medicating again after she ended her long-term mission. She wasn't quite so bad with it to start, and she was able to convince herself she didn't have an issue every time she went to bed with whiskey warming her belly. She was even able to keep it hidden well from Nik--or, well enough. She could pass it off as a healthy appreciation, just some light social drinking, a glass of wine with dinner, maybe a mimosa at brunch.
She met a nice man named Mathew Starnes and found love again with him. After a rough argument and almost break-up, Nik came home to find Sarah drunk off her ass--again--and she made it a project to keep her mom away from alcohol, and for a while, Sarah was able to stick with it. She attended a few scattered muggle AA meetings, and she only drank when she was with someone she trusted to stop her after one drink, and she was okay. She and Mathew got married and adopted a rebellious teenager named Kinzie, who took quite a while to grow on Mathew. She and Nik were close, and she eventually warmed up to Sarah, and when Sarah and Mathew had a little boy named Justin, she doted on him...until she was killed by a vampire.
Sarah had a rough time after Kinzie's death. Her greatest fear is losing her children, and for the longest time she had trouble accepting it, even once the body was found. She had Justin though, who was still so, so young, and he was the biggest part of her staying sober through it. Her relationship with Mathew had already started going down by this point, so between her dedication to her baby, Nik's incredible...helicopter parenting, and a lot of time struggling through muggle AA meetings, she made it. She knows it doesn't technically count since she did still drink in small, controlled amounts, but she's proud of having stayed sober for eleven years straight.
She made it through her divorce as well, and had no trouble being a single mother again.
When the scrofungulus epidemic hit, both she and Justin contracted it. If she thought having one child killed was bad, watching another slowly die was even worse. Logically she knows that there's little she could have done to prevent Justin from getting it, but she can't help but wonder if things would have gone differently if she'd just gone to St. Mungo's at the first symptom. But she was a mother--of course she thought she could handle a little flu. But then it got worse, and when she finally took him to the hospital, she was symptomatic as well. The hospital was nice enough to keep them together, but damn was it hard to try to comfort her son when she felt on the brink of death herself--she tried, though. She tried so hard. And even when she knew, when she just felt that he wasn't going to make it, she kept trying, hoping that if she just...loved him enough, he would make it.
But he didn't.
She went straight out of the hospital and into the bottle, and nothing was going to stop her from drowning her sorrows the best way she knew how. She took leave from work and went on days-long benders where she refused to speak to anyone except the cashier at the liquor store, and it was a miracle she pulled herself together enough for her son's funeral.
She was barely able to claw herself out of the hole enough to actually go back to work, but she did it, just barely. For three years after Justin's death, it wasn't uncommon for her to drink at work, or to spend her weekends drunk. The worst times were when Nik was on a mission, or when she came back injured. Sarah was always just...so scared that one day Nik wouldn't come back, or that she wouldn't make it, and it drove her almost mad.
It was actually Nik's divorce from her wife that helped bring Sarah back to sobriety. Nik's relationship with Tori wasn't healthy; she was dependent on her for support when she had nightmares or her PTSD decided to rear its head again, and once Nik was alone she had a rough time adjusting to dealing with her problems on her own. Sarah had to make lots of late-night trips just to make sure she didn't lose another child, and she needed to keep a clear head about her for that.
Sarah has been sober since she was fourty-nine.