Some TMNT stuff was always meant for grownups.
In the Mirage TMNT universe, Sloane is a former human teenage girl, now a werewolf, who at one time was a friend of Shadow Jones in New York City. She is a central character in both Tales of the TMNT volume 2 issue 7: Darkness Weaves and in the followup miniseries Raphael: Bad Moon Rising.
According to Darkness Weaves, late one night, Sloane met up with Shadow, who had snuck out from her uncles and grandfather's home to attend a clandestine Lilith concert with her. At the concert, while Lilith was singing, the singer cut her wrist and drained some of her blood in a toblet, which the concert attendees passed around to ceremonially drink. Sloane drank, but Shadow hesitated, and still hadn't drunk when Lilith, Sloane and most of the concert goers begin transforming into werewolves. Shadow's uncle Raphael came to rescue Shadow, handed her a weapon, and the two trained ninja tried to fight their way out. Shadow was disturbed when one of the werewolves she stabbed turned back into the naked human form of her friend Sloane, who then died before her eyes. The werewolf Lilith carried off Sloane's body and promises revenge against Shadow for the death of her pack mate.
According to Bad Moon Rising, Lilith managed to resurrect Sloane, but she came back wrong, missing part of her soul. Sloane had become a member of Lilith's Sisterhood and became a close friend of Lilith's daughter Lucrezia ("Lulu"), but Sloane secretly resented Lilith for bringing her back with only half a soul. Sloane began a romantic affair with Lord Chiton, ruler of the kingdom of Atlantia, who was Lilith's ex-husband and Lulu's father, even as Chiton was married to his new wife Oceana. Chiton, Sloane and Lord Incubor conspired to ruin Lilith's life, first by kidnapping Lilith, then turning the rest of the Sisterhood into zombies, then casting Lilith as an incompetent mother to play in Chiton's favor during their next child custody battle over Lucrezia. As part of the arrangement, Incubor would retrieve the missing half of Sloane's soul.
Sloane, with the unwitting Lulu in her care, stayed away from Lilith's Den during the kidnapping, and claimed to having escaped the same fate as Lilith and the Sisterhood. The two traveled to the Jones Farm in the normal world to beg Raphael and Shadow to help them rescue Lilith. They traveled together to Nocturna to investigate Lilith's disappearance, starting with Lilith's unoccupied den, all the while with Sloane remaining in secret contact with her co-conspirators. While they were inside the den, a giant barn owl ripped the structure from its foundations, carried it across the sky, and dropped it into the open ocean where it was caught and enveloped by a giant jellyfish. When they woke up, they were in the underwater kingdom of Atlantia, in the care of Lord Chiton who had "saved" them. Chiton "promised" Sloane and Lucrezia the resources of his kingdom to "rescue" Lilith, and gathered a great army to face Lord Incubor's forces in a staged but genuinely bloody battle. But when the battle began, Raphael, Shadow and company were prevented from leaving their guest quarters, provoking the hotheaded Raph into attacking the guards and starting a brawl where the friends had to fight their way out, with Sloane "helping" along the way. With Lulu's help, they traveled to the tower where Lilith and the Sisterhood were being kept, and Incubor's succubi feigned resistance against them. Lilith was rescued, but her werewolves had been turned into zombies and could no longer lead normal lives.
The outcome convinced Lilith to make peace with her former enemies Raphael and Shadow, and made Chiton into the noble hero who went to war to rescue his ex-wife. But Raph and Shadow were already suspicious of how everything had gone down, and they followed Chiton and Sloane to a hallway where they were caught meeting with Incubor. Chiton and Incubor were friends, Sloane was actually Chiton's secret mistress, and they had just been using Raph and Shadow as part of their plot. Raph's suspicions of Sloane's bad character were vindicated, and Shadow's renewed friendship with Sloane was soured, but the uncle and niece were given no choice but to keep the conspiracy secret in exchange for being allowed to travel back home to their own world.