The city must have been hidden somewhere backstage. So it wasn't Siberia, but rather the theater stage that lay between my parents and the city of their dreams.
I found this passage to be very romantic in its usage of language, and to have a deeper meaning behind it. Tawanda mentions how her parents were separated from the city of their dreams by the "theater stage," not by Siberia. This puts a very ironic depiction in her head, because the stage, or the "world" became the separation for her parents and the city they always dreamed of. This could be an example of the rapid change in transportation and immigration over generations, and how borders can be confusing and in flux.