visiting paris for first time in mid september

This is the busiest month and most expensive month for hotels so your first task is to line up lodging that you want.

Then identify the things you want to do and begin lining up tickets. A couple you might not have thought of - the Louis Vuitton Fondation museum -- I don't know what is on next September, but they always have wonderfully presented exhibits and it is a good place for lunch. Another ticket you need well in advance is for the Dior Gallery. My daughter and husband did it this April and really thought it was terrific. Something that gets overlooked that I find terrific is Bassilica St. Denis where the tombs of the Kings of France are and is on the metro just outside Paris. If you are into wine, a visit to a Champagne house and their cellar in Reims makes an interesting day trip. It is just 45 minutes away by tGV. We did Taittinger and loved it. Another great day trip is Monet's House and Garden at Giverny, easily done by train from Gare St. Lazare.

But mostly 'what is your dream of Paris' and do that. If you are stuck lots of guide books have 3 days itineraries etc and that is a place to start.

Welcome to the forum. Can you please give us some more information so we can help you?

What type of advice are you looking for? Hotels, restaurants, sightseeing, transportation, walks???

For starters, scroll through the forums for "France" and for "Trip Reports". You'll find all kinds of advice.

Also, stop by your local library or bookstore and pickup a guide book or three on Paris: Rick Steves', Fodor, Lonely Planet, Eyewitness or whatever catches your eye.

Here are many suggestions from the host of this site https://www.ricksteves.com/europe/france/paris

And here are posts with similar questions from the past year, lots of ideas https://search.ricksteves.com/?button=&date_range=1y&filter=Travel+Forum&query=first+time+paris&utf8=%E2%9C%93

Is this a party of two or a party of three?

How long will you be there? Please provide more info for advice. Interests? Budget for rooms? Any preferences for amenities? It is hard to provide answers for such a broad question. I recommend getting a guidebook or two from the library to narrow down your expectations. When you picture yourself in Paris what do you see?

Here's what you do - you watch as many Youtube videos as possible, including of course Mr. Steves. Les Frenchies and Jay Swanson too.

And you buy and study his latest guidebook cover to cover. If you're completist, also get the Frommers guide.

The age discrepancy means you'll need to compare and contrast various options, as they say.

Hopefully you have your flights and lodging lined up since you are traveling in about three months. I would make a list of sites/things that are must dos for you both and then group them together by location on the same day, so you aren't crisscrossing Paris all the time. For example, I would pair Sainte Chappelle and Notre Dame on the same day as they are super close.

Also, I plan at most two activities/sites in a day - one morning and one afternoon. Some days it is just one if I am going to go to a place like The Louvre because I don't know how long I am going to be there; personally, I can spend 5+ hours at a museum.

Since it is Paris, make sure to leave time for lingering at a cafe with a glass of wine (or coffee if you don't drink) and enjoying the cafe culture. It's a nice way to take a breath and relax in the late afternoon...at least to me.

If we know how long you will be there and some of your interests, we can give some more specific suggestions/advice. Have a great trip with your daughter!

Just a note for first-time posters. The forum is made up of real persons who reply. It is hard to answer quiries that are presented as a wide, google-type search. We need context and some parameters to be most helpful. Regarding hotels and eateries, there are hundreds of lodgings and thousands of cafes, restaurants, etc. Likewise, a plethora of sights to see. Where would a person replying begin?
The suggestion to do a little research, whether through guidebooks, podcasts, tv travel shows, is a good one. The Paris experience can be overwhelming and it is wise to do some narrowing-down ahead of time. Then forum answers can be the most useful to the original poster.
I wish both of you a wonderful trip to this enchanting city, which Rick Steves refers to as the capital of Europe (and I concur).

September is a good time to be in Paris; it's not as expensive as October, and the weather is better. But you really need to think about what you want to see. Pick three "must have" things, and plan around those. And for suggestions it helps if you let us know what you prioritize; food, tourist attractions, art, parks, flea markets, etc.

Agree with all of the above. Giverny is a great day trip, and the garden will be spectacular in September. Followed by the Orangerie, of course, to see the water lilies.
Don't over schedule yourselves. One of the best things about Paris is just walking around and taking in the architecture and the gardens, sitting outside the cafes and bistros and people watching, etc.
Take as much time as you possibly can. I know most Americans have very little vacation time and are often pressured not to use it. You're going a long way at great expense, so make it worthwhile.
A friend recently used Costco's travel service to book a trip with his son to Paris and Amsterdam over spring break, and he was very pleased with it. It covered airfare, transfers and hotels. Probably cost him more than it might cost one of the Forum regulars, but it eliminated a whole lot of planning. So if you're a member, it's worth taking a look at.