In mid-2018, Ms. Roberts was working as a personal assistant to Mr. Biden, according to a person close to her and messages from a cache of Mr. Biden’s files. Their daughter was born later that year, but by then, Mr. Biden had stopped responding to Ms. Roberts’s messages, including one informing him of the child’s birth date. Shortly after their daughter was born in November 2018, he removed Ms. Roberts and the child from his health insurance, which led Ms. Roberts to contact Mr. Lancaster.