As other posters have noted, I'm pretty sure this is a regionalism or colloquialism. The present continuous tense (e.g., "is sitting") per Teach Yourself Hindi, p. 258 (ISBN 0071420126) is root + रहना (e.g., बैठ रही है), while there's no provision for the above form ("बैठी है)". Can someone at highest fluency in English and Hindi comment on this?
Is this supposed to be translated "is seated", instead? That would make more sense with the adjective बैठा instead of trying to map the adjective to a gerund.
Why would this not be "the girl has sat on the table" (present perfect)? I am confused as to when rahana is needed before hona. I thought that rahana made it present continuous (I am sitting), and that in this case it would be present perfect conjugation. This is the source I am referencing: http://www.hindiverbs.com/tenses.html