There is a tram, the hone Express, from Lyon Airport to Lyon Part Dieu Station. I have not used it myself but it s reasonably frequent if rather expensive in relation to the length of the journey. From Lyon Part Dieu there are several trains each day direct to Digeon. You can find times on www.voyages-sncf.com. Although advance booking is not actually required on these trains, it might be a good idea for you/her to do so, so that she has something to show to SNCF staff if she wants assistance in finding the right place to go as Part Dieu is quite a large and busy station.