"She is not there."

Translation: Není tam.

[GehorLef]

Can I say Ona není tam?

[Zygro]

No. Generally, if the subject is a pronoun, you leave it out (the form of the verb will provide necessary context).

However, a correct way to say it would also be "ona tam není". This version is emphasised, contextual and not often used. One example where it would be used is "Ona tam není, ale on je" (she's not there, but he is)

[VladaFu]

There are many stentences in this course wher the pronoun is allowed although it is not the first variant you would use.

For example "Není tam ona." has been already accepted for some time.

[VladaFu]

Should be possible.