Assuming you're leaving from the TGV station at the airport, you'll need to take the free shuttle from CDG1 to CDG2. You should have plenty of time, but not necessarily time to spare...
If you need to take the TGV at Montparnasse, Gare du Nord or Gare de Lyon, then you might need to reconsider staying one night in Paris and take the morning train to Lourdes...
BTW, Welcome to FT!!