As a consequence of her body still being on the beach, Amelie is unable to age, and looks now as she did ten years prior. Carrying on her mother's legacy, Amelie embarked on an expedition to bring her message of unity to survivor communities across America, convincing many of them to join the UCA and connect to the Chiral Network.

She protected the expedition team while they looked for survivors, using her preternatural ability to anticipate craters and BT-occupied territories to circumnavigate the areas. Three years into the expedition, Amelie and her team reached Edge Knot City, whereupon the team was wiped out and Amelie was captured by the Homo Demens.

She is now being held within the city as an insurance policy against the UCA, but is allowed to use Edge Knot City's facilities and communicate with her UCA allies in Capital Knot City. Die-Hardman and Amelie want Sam to finish what Amelie started and rescue her from Edge Knot City.

Should she successfully be brought back by Sam, Amelie intends to take up the presidency of the United Cities and continue realizing her mother's vision for the country. Amelie is able to sense BT's to great effect, and can circumnavigate craters and BT-occupied territories entirely. Amelie, as the Extinction Entity, is ultimately the one responsible for bridging the gap between the living world and the Beach, and is therefore the cause of the Death Stranding.

She can potentially force all beaches to merge with her own, and the Chiral network. This would allow untold numbers of BT's to pass onto Earth and ultimately cause a chain reaction of Voidouts that would permanently end life on Earth, an event called the Last Stranding. Amelie has resurrected dead beings, such as Sam. She is the one responsible for DOOMS abilities, by sharing her visions of potential extinctions with others, and allowing them some measure of her connection with the other side.

Source: https://deathstranding.fandom.com/wiki/Amelie