At the age of eight, she began to take acting class with Luis A. Negro, and dancing class with Beatriz Trujillo.
In 1957, she made her acting debut at Teatro Tapia, in a play named Mientras los Ninos Juegan (While the Children Play). That same year, she debuted on television, with channel 2's production of Los Amigos de Pinocho (Pinocho's Friends).
Rosaly began to take singing class when she became a young teenager. Then, she participated in such plays as My Fair Lady and The Sound of Music, the latter of which allowed her to share the stage with another Puerto Rican acting legend, Camille Carrion (who is the sister of Richard Carrion).
Rosaly went to college and then participated in the Telenovela named El Retrato de Angela (Angelas Photo). In this soap opera, she played a mute girl.
Soon she married Jose Gilberto Molinary, with whom she had 2 sons and a daughter. Her daughter, Alfonsina Molinary, went on to become a famous actress herself in 1989; when she was the star of television comedy Maripili, a show that resembled Clarissa Explains it All in format, and a famous opera singer in Philadelphia.
Rosaly made a number of soap operas in the 1970s. However, the one she is remembered most for, and the one that helped her internationalize as a singer and actress was 1978's Cristina Bazan, alongside Jose Luis Rodriguez and Adamari Lopez among others.
She signed with Velvet Records soon after, and began touring all over Latin America, to promote her two albums under that label. She also attained considerable fame in Spain. Later, she would sign with CBS International and record two more albums for them.
Rosaly would soon move from Telemundo Puerto Rico to WAPA-TV. There, she participated in three other soap operas. By 1980, rumors of a romance with world boxing champion Wilfredo Gomez ran across Puerto Rico.
As the 1980s went along, Rosaly began to retire from acting in soap operas and became a television interviewer and show host, back at her original channel of Telemundo Puerto Rico, then known only as Telemundo Canal 2. In 1989, she acted alongside Tommy Muniz in Jacobo Morales' Lo que le Paso a Santiago, which was nominated for an Oscar as best foreign film..
During the 1990s, she dedicated much of her career to acting in various critically acclaimed theather plays. But she also made two more movies: 1993's Shortcut to Paradise, and 1994's Linda Sara, alongside Chayanne.
She has received multiple honors, among them, the Puerto Rican Culture Institute (ICP), dedicated their 1997 film festival to her, honoring her 40 years as an actress.