Jenny is the balancing force between her polar-opposite brothers. She very much has eyes for Billy Creel, and he for her, which is why Billy comes to the restaurant to eat. Growing up somewhere out east,  her parents died when she was a child, and she and her two brothers Leo and Andy raised themselves.
According to Colin Moriarty's files, Jenny Stahl was almost raped by, or had some kind of affair with Jericho. Despite having found this evidence, the Lone Wanderer cannot ask Jenny about it. There is, however, an audio conversation between Jericho and Jenny about how it was a long time ago, and how he "knows what her problem is...". If waiting around while the two get together periodically, one can hear Jericho trying his luck again, but is unsuccessful every time.