Bit of a long AU idea but please bear with me (this takes place mainly in the show universe).
What if there was a another reason Penelope took up Whistledown? Imagine thirteen year old Penelope finding out she has a half-sister, eight years younger than her when she hears her father talking with his solicitor who reminds him that he needs to pay the young girls uncle or he'll let the news slip. Somehow Penelope manages to convince the solicitor to take her with him to visit her sister and the man reluctantly agrees (knowing the youngest Featherington girls absence will not be noticed) but insists she dress in servants clothes. Penelope meets her sister Felicity as well as Felicity's female cousin who is a year older than Felicity and tells them who she really is and thus begins a long time of secret meetings.
It's right before her first season that Penelope realizes how bad the family finances are when her father isn't able to pay the money Felicity's uncle is asking for and the man threatens to sell her sister to a brothel once she begins bleeding, as he has four other mouths to feed. Que Penelope starting her career as Whistledown to help keep her sister safe.
Unfortunately, come postseason 2 she finds out Felicity's uncle sold his one daughter to an older lord, since she looked similar to his wife who was unable to conceive. Cue season 3 where Penelope is trying to find Felicity's cousin, dodging Colin's advances, and avoiding detection of the queen.
It all becomes to much when Colin does find out and does not take it well at all right around when they find Felicity's cousin. The girl is unfortunately pregnant and due to give birth soon and Penelope decides she has no choice but to reveal herself to the queen in order to ensure Whistledown ends while also getting Felicity and her family out safely.
Penelope goes to Lady Danbury and reveals the truth to her (though not about her family situation) and the woman tells her what two options the Queen has proposed to her for if Whistledown should reveal herself. 1) Be banished from high society and London and never write again or 2) be allowed to keep writing but only for the Queen and only what the queen wants. Come the day Penelope reveals herself to the queen in a private audience, both the Queen and Lady Danbury are shocked when Penelope chooses option 1 and even more so when she signs the agreement.
That night, during a ball held by the queen, Felicity's cousin dies giving birth to a baby girl and asks Penelope to look after the child. Penelope, with help from the solicitor, escape into the night with Felicity, her three young cousins, and the newborn baby. They move to a small town, far from London where Penelope takes up a position as the town's first school marm for their newly built school house while also helping out at the tavern some nights.
Of course the town people believe Penelope to be the mother of the baby girl, especially since many women in the village came to settle here as the result of their children being bastards. But the town protects their own and so Penelope and her family are kept safe. She learns to cook from the ladies of the village who adore how patient Penelope is with the children, and Penelope also develops a friendship with some of the other girls in town, who take her under their wing.
Back in London, Colin and Eloise told their family who Whistledown is and the Bridgertons are not that happy with Penelope. That is until the ball that night, where Queen Charlotte triumphantly announces the death of Lady Whistledown claiming the person came forward on their own and as such, Queen Charlotte will not reveal their identity. At some point during the ball, she slips Eloise the 1,000 pounds saying that Whistledown had said the girl figured her out first and deserved the prize money. Except it feels more like blood money to Eloise who has felt sick since hearing the news.
Five years go by, Penelope keeping only in touch with Gen, her solicitor, and Phillip and Marina (who she reconciled with after telling the truth to Marina pre season 3). Her life is nothing like the one she had growing up, but it's full of warmth and love with her siblings and child by her side.
That is until Eloise finds out Penelope is alive (maybe she spotted a letter at Madame Delacroix or Phillip let it slip in his letters).
Cue Penelope, with her five year old adopted daughter clinging to her skirts, hearing a frantic knock at the door and answering it only find Eloise Bridgerton looking shocked as if she'd seen a ghost and letting out a "you're alive," before fainting.
Penelope is then left to take care of Eloise but of course this results in a few other Bridgertons showing up at her house. It doesn't help that when Colin shows up, the town believes him to be the father of her young child and are none too pleased with him (she's tried telling them that the baby was her dead sisters but no one ever believed her!). There are also rumors of a certain noble looking for his missing child.
This is a very good story and I hope you guys anyone please write it and send me the link I will give you a signal boost