The 22-year-old cheated on Pattinson with "Snow White and the Huntsman" director Rupert Sanders.
"Kristen is really stressed out and nervous about making her first public appearance at the upcoming Toronto Film Festival. But it's not the premiere that she is worried about, it's her pending conversation with her 'On The Road' co-star Tom Sturridge," contactmusic.com quoted a source as saying.
"She wants to have a private conversation with Tom and try and convince him how sorry she is and how she wants Rob back. She is more concerned with her conversation with Tom than with the premiere of 'On The Road'."
"The only thing that matters to her right now is getting Rob back and she knows the way to get to Rob is through his best friends," added the source.
Stewart is said to be planning to ask Sturridge's fiancee Sienna Miller for advice.
"She wants both Tom and Sienna to know that she never meant to hurt Rob and that she is not an evil person. She is hoping and praying that Tom and Sienna will understand and forgive her. And that they will help her win Rob back," said the source.