In her son montuno style, she has the bass line play the root of the chord in the next measure on the upbeat, or "and", of 4. The mambo bass line with the accents on the upbeat of 2 and on 4 is illustrated many times in her book "101 Montunos". BIAB has no mambo style with the accent on 4, that I know of. In a simple C7 montuno, the bass would be playing G on the upbeat of 2 and C on 4. The clave should be a 2-3 pattern.