。
She got into a taxi.
Literal
She [topic-は] taxi [onto-に] boarded.
乗る ('to board, get on, ride') is the verb for boarding any conveyance — vehicles, animals, even abstract things like waves. The vehicle takes に, marking the goal of the boarding action: バスに乗る, 電車に乗る, 馬に乗る, 波に乗る. This contrasts with English 'get in (a taxi)' / 'get on (a bus),' which fork by vehicle type — Japanese unifies them all under 乗る+に. The opposite, 降りる ('to get off, alight'), takes を or から depending on what's being departed.