It is a requirement of unaccompanied minor transit that the guardian
go to the gate and wait until the plane is away. So I am assuming it
is possible.
This isn't always the case when it comes to departures for international flights on airports outside the USA.
Under the section "children traveling outside the US," American says "you may not be able to escort your child through security in some airports. If this is the case, a team member will take your child to the gate and stay with them until the flight departs." I also looked at Air France (since their hub is CDG, so I would assume procedures are broadly similar) and it says that "an Air France member of staff will accompany him or her to the aircraft."
Of course, in all cases, the parent/guardian does have to stay at the airport until the flight departs, even if they aren't allowed to the gate.
Especially because there are exit passport controls at CDG, I think that you probably will not be able to accompany your granddaughter to the gate and should prepare for this; if it ends up that you can, well, that's a pleasant surprise.