Thank you all! We already have tickets from LAX - CDG - LAX on United. We got a great fully-changeable fare a few months ago right before the airlines started to change their Covid policy.
That said, I took a look to see if it's cost-efficient to change it up and fly straight to Marseilles, then straight out of Florence back to LAX. (We are going from Aix to visit our daughter while she studies abroad in Florence for 4-5 days.)
Two new airline tickets would cost us an additional $1,511 total to fly into Marseilles and straight out of Florence. So... even when I add on two train tickets from CDG to Aix and two plane tickets from Florence to Paris, I think I'm way ahead financially if I keep what I have. Hmmm....
$150 TGV from CDG to Aix + $80 flight on Vueling (includes a checked bag) nonstop from Florence to Paris. A bit of a hassle but we'll save a good $1,000 and have a day/night in Paris! :)