Various possibilities make this outcome viable. A pandemic may delay the 2020 presidential election in many states, after which both incumbents Donald Trump and Mike Pence have expired terms and Nancy Pelosi assumes the office via line of succession after being re-elected by a less-affected California. Alternatively Joe Biden wins the 2020 election but is at high risk to exposure, succumbs, and leave his vice president to assume the office (who is presumed female e.g., Elizabeth Warren). If a female US president is instead elected directly or assumes the office for reasons not directly caused by a pandemic, this bet would be lost.
Challenge Martin S McCormick to a bet on this prediction!