She does not know is the the most correct. A tip for IELTS I ask my students not to shorten words as it is easy to confuse the reader if mistakes are made. As time is short, in IELTS, being understood is more important than grammar. Good spelling and good sentence structures are all that is needed to use language well. The easier it is for the reader to understand the information the more likely they are to continue reading. I hope this helps Have fun

She doesn't know

The latter is correct though the former is often used in certain areas of English speaking countries. 😎

The second one

She doesn't know.