While Sienkiewicz's family originally came from Grodno, she was born on 14 February 1935 in Ostrów Mazowiecki.

Sienkiewicz debuted as an actress two years earlier, on 1 September 1955 at the Studencki Teatr Satyryków (STS; Student's Theatre of Satirists).

A famous Polish movie critic, Krzysztof Teodor Toeplitz described her as a pink phenomenon of STS (różowe zjawisko STS-u).

[3] From that moment she appeared in more than 20 movies, including Jutro premiera (1962), Lekarstwo na miłość (1967) and Rzeczpospolita Babska (1969).

[5] As a singer, Sienkiewicz mainly sang poems by Agnieszka Osiecka, Konstanty Ildefons Gałczyński and Olga Lipińska.