If your program can export MusicXML, that is the very best way to get the notation into Sibelius.

If not, using PDFtoMusic Pro is the next preferred choice. The steps are:

1) Print a PDF file from Nightingale, Lilypond or other program.
2) Use PDFtoMusic Pro to convert the PDF file into a MusicXML file.
3) Import the MusicXML file into Sibelius.

This is usually much more accurate than scanning and saves an enormous amount of time over re-entry.

Other alternative include:

1. In Lilypond save to PDF format, and then use one of the three choices:
   • print & scan into Photoscore
   • Import PDF in PhotoScore
2. Export from your program to MIDI and then import MIDI in Sibelius.

Unfortunately, the Music XML Guitar Pro outputs cannot be read by Sibelius.
There is however hope: A free clone of GP called TuxGuitar, which is available for all major OSes outputs valid MusicXML!