Amber Stein is a Sim who appears alongside many Sims who are used in various promotional materials of The Sims 4. She appears in many official screenshots and videos. She can be downloaded from the gallery; likewise, she is also one of the default Sims available in the Create a Sim demo.
There are, however, two official EA/Maxis created versions of Amber that can be downloaded from the Gallery: one version has Amber in a household on her own; the other, called the Best Friends household, has her living with Armand DiAggro (her best friend from the "It's Amber" trailer) and an alternative version of June Kay.
Several videos and renders seem to show Amber romantically involved with another promotional character, Sean Sullivan: at one point in the "It's Amber" trailer the two are shown engaged in a marriage proposal.