Elizabeth,
According to the CDG web site, 90 minutes is ok for European flights - http://easycdg.com/passenger-information/check-in-departures-cdg-airport/
And, since you are near the Eiffel Tower you can take the 45 minute train from Champ de Mars to CDG. Note that the train makes two stops at CDG so you need to know which terminal your flight departs from. The train from Paris first stops at Terminal 3 then stops at Terminal 2.
To determine which stop you'll want, see this page which lists the terminal each airline operates from.
http://easycdg.com/airport-guide/which-terminal-paris-cdg-airport-charlesdegaulle/
There is a shuttle rail service called CDGVAL that runs in the airport between all the terminals so you can recover if you get off at the wrong terminal.
Trains from Paris to CDG run every 6 to 15 minutes. Tickets are 10 euros and they can be bought from the machine with coins or credit card.
In April I took the RER from Champ de Mars to Notre Dame station and there switched trains to go to CDG. My only problem was getting to the right track at Champ de Mars. At Champ de Mars, there are two sets of stairs leading from the sidewalk down to the tracks. The stairs you need are closer to the river, not those closer to the road. Easy peasy.