Danielle Gilchrist is the daughter of the caretakers of the Meriweather estate, and a close friend of the Saybrook family.
She was once the best friend of Aster, although the two had a falling out after Aster discovered Danielle's alleged affair with Mason Saybrook. It was later revealed that there was never an affair, but rather, Danielle and Mason were close that Summer because she found out she was really Mason's daughter and another heiress to the Saybrook fortune.
Danielle grew up around the Saybrook family, with her being around so often that the Saybrook's considered her family. She was particularly close to Aster, who she considered to be her best friend. The two were often confused as sisters, something both girls went along with when they were out and about and no one knew who they really were. Danielle introduced Aster to alcohol, prank calls, and men. One day, Danielle gave her a diamond tennis bracelet as a gift.
However, years down the line, over that Summer, Aster and Danielle had a falling out. Aster witnessed her father Mason staring Danielle in a very revealing bikini and believed that the pair were having an affair. This lead to a huge falling out behind Aster and her.
Danielle and her mother Julia attended Steven Barnett's funeral, where a saddened Danielle received a hug from Corrine. At the funeral, Aster could barely look at Danielle. After Natasha made a remark about Steven's death, Danielle and her mother returned to their seats to allow the Saybrook's some time alone. She also attended Poppy Saybrook's funeral with her mother, and seem completely distraught over Poppy's death.
About a year later, she gave Aster the new-employee presentation for Saybrook's Diamonds.
On the bridge, it was revealed that there was never an affair between Danielle and Mason, but rather, Danielle was really Mason's daughter. She had found out five-years prior to the events of The Heiresses when they were together during that summer, but Mason made her promise not to say anything. Julia expressed rage over this, saying that Mason was a horrible father and person to her, letting her grow up on the grounds of his home but not his real home, hang out with his daughter, share clothes with her, and much more. But he never claimed her as his own and allowed Danielle to have the same rights as his other daughter. Danielle, heartbroken, told her mother that she had made peace with that and was no longer upset with it - and she thought her mother had as well.
Julia admitted that she wanted to earn her rank in the family and make everything right for her daughter, and at the end-of-summer party, she did just that when she killed Steven Barnett. Danielle was horrified by the revelation and tried to get her mom to stop talking and waving her gun around, but eventually stood there silent just sobbing as her mother then admitted to killing Poppy, attempting to kill Penelope, and so much more. Danielle, now heartbroken, refused to stand with her mother and was both sad and angry that Julia had tried to frame her for the murder of Poppy (by wearing her dress, using her pass, etc) by using the surveillance video.
Danielle and her mother argued and talked about the deaths and murders, before Danielle stood in front of her cousins and sister, and told her mother that if she wanted to kill them they'd have to kill her as well. Julia was willing to do this after she realized her daughter was just like the other Saybrooks and was ready to kill them all when the FBI showed up and stopped Julia. They tried to arrest her as Danielle screamed from the bridge and sobbed, watching her mother climb over the guardrail. Julia waved her gun and was shot by the police. She said goodbye to her daughter before falling backward into the water below.
In the aftermath of the incident at the bridge, Danielle remained silent to the press despite them publishing numerous headlines about, "The Secret Daughter" and many other secrets that were based on little information and what they knew about the bridge incident. She also started communicating with Aster a little more, as Aster was trying to get used to the fact that they were really sisters.
Danielle is described as being a beautiful young woman with a slender build, pale skin, and red hair.
As children, Aster and Danielle were extremely close and would often hang out with one another whenever they could. When they went out places, people would often mistake them for sisters due to their same striking blue eyes and close-knit relationship. The duo played along with people's misconceptions and often used this to further whatever they were doing at the time (shopping etc). They remained close into their teen years, and Aster gifted Danielle with a diamond tennis bracelet on her birthday, courtesy of her families diamond company.
While they remained close, the summer prior to Steven Barnett's murder, Aster began to suspect that something was off with Danielle and her father. She suspected that Mason was having an affair but wasn't sure of whom it was with. One day, while the girls were at the pool, she caught Mason staring at Danielle who was wearing a revealing bikini. This confirmed Aster's suspicions of Danielle having an affair with her father and cut her out of her life completely.
They interacted several times after this, at Steven's funeral, Poppy's funeral, at Saybrook's Diamonds where Dani gave Aster her new-employee presentation and a few other locations. However, Aster remained cold and distant towards Danielle. In the end, Aster learned the truth about that summer along with the true nature of Mason and Danielle's relationship. When Julia (Danielle's mother) had them on the bridge at gunpoint, she revealed that she had an affair with Mason that resulted in the birth of Danielle. She was infuriated with Mason for hiding Danielle away and robbing her of her birthright of being an heiress. Danielle had become aware of her true father during that summer, and that was what she and Mason were whispering about. Aster was shocked to learn that Danielle was her sister, and this changed a lot between them once again.
A year later, Aster had fully accepted her as her sister and even invited her to live in the Meriweather Estate. Also, Danielle forgave Aster for cutting her out of her life and assuming the worst of her. Aster also helped Danielle become an heiress to the company, and boost her social status. While both women had a lot to work on as far as trust went, they were headed in the right direction by the end of the novel.