 After serving 16 years in the Chamber of Representatives, Mejía ran for Senator of Colombia in the 2002 legislative elections as a Liberal candidate heading the Electoral List 648 that also included Ernesto
Zuluaga Ramírez, Atilano Alonso Giraldo Arboleda, Miguel Ángel Pérez Gamboa, and José Albeiro Gallego Agudelo.In the national general election she received 55,087 votes, most of them from the Coffee-Growers Axis region, that represented 0.535% of the total national votes earning her a seat in the Senate.In 2004, following a national debate about amending the constitution to allow for a second presidential term, a motion widely popular among Colombians and sought by the sitting President Álvaro Uribe Vélez, Mejía voted in favour of the re-election amendment and went against the official position of her party which opposed the re-elections of Uribe that demanded that all its members vote against it.