If you resend, DocuSign will send notifications to all recipients at the current routing order who need to act on the document.  DocuSign will not send notifications to those who have completed their jobs in the envelope.  DocuSign will not send notifications to those in future routing orders.

I sent an envelope to my boss which needs an updated signature by her. Can I create a copy or forward it to her again, so she can sign it correctly, or do I need to start from scratch and create a new envelope?

As signature is applied you can create a copy of the document this will copy the workflow and the fields so you can update and amend the fields and send again. ​

Thank you Robert, I was in fact able to resend, and obtain a corrected signature.

Is it possible to choose the persons to resend, leaving apart someone who hasnt yet completed his job?