The internet lied to you (or, the actual first female serial killer in the US)
If you google ‘First Female Serial Killer’ the name that nearly always pops up is Aileen Wuornos but the distinction actually belongs to Lavinia Fisher (within the US at least). Born in 1793 Fisher lived in South Carolina and owned an inn with her husband. (Side note: inns seem to be a popular occupation for murderers. You can file that under ‘avoid inns’ or ‘possible careers’, no judgement).
Fisher would chat up guests in the hotel, trying to figure out if the guests were wealthy and worth her murdering time. If she determined that they had money she would send up a glass a poisoned tea (lady first, killer second).
Because she was charming she escaped investigation for a long time (another tip, be charming and avoid suspicion) until 1819 when a group of local vigilantes stood outside the inn, trying to catch her in the act and other find other criminal activity. Instead, the man was beat up and taken to the local gang, where he found Fisher waiting. He expected her to help her, instead she choked him and bashed his head through the window (savage). He escaped and alerted the police.
After another potential victim escaped Fisher, her husband and their two accomplices were taken in.
The court found them guilty and, while waiting for appeal Fisher and her husband tried to escape. In a tale of true love, he escape but when he learned that she couldn’t he returned to the prison to serve out the sentence with her.
They were executed later that year.
Fisher is nearly always forgotten about when we talk about female serial killers, either because of the time frame or because she killed with posion (more popular among women than men for murder). But she’s worth knowing about because she was the first proven female serial killer in the US.