Birthday in Paris

She is having a birthday in Paris. That is a wonderful gift! We travel with our daughter and she has had three, soon to be four, birthdays in Europe. Make a reservation at a nice restaurant, let them know you are celebrating a birthday. Tell them you want a surprise with candles at the end. They will do the rest. Your hotel can help if you can't do this. For a real treat learn to sing Happy Birthday in French. It's not hard to learn and don't be surprised when the entire restaurant joins you!

I have read about a bike tour that a friend took her teenaged granddaughter on to Versailles. It looked like a lot of fun and not too difficult to do. A nice breakfast at Angelina's restaurant across from the Tuileries gardens would be a treat too!

It would be helpful if you could include a little more about what your daughter's interests are.

Or, perhaps you could get her to give you some ideas about what she would like to do.
Pretty sure that your 15-year old would go along with whatever was suggested.

We were in Paris when I hit 71 last spring. My wife gave me a postcard with a VanGogh painting on it; and paid for a cab when it started raining. These are not suggestions.

How wonderful to be able to spend your birthday in Paris! I have yet to go there. I also think it really depends on your daughter's interests, but you could never go wrong with going to a nice restaurant. I think a river cruise, day or night, would be memorable too. I would suggest checking out the website http://en.parisinfo.com for more ideas. I quickly browsed through it, and it looks like it has a lot of information on all kinds of events, shows, and other things to do.

We were in Paris when I hit 71 last spring. My wife gave me a postcard with a VanGogh painting on it; and paid for a cab when it started raining. These are not suggestions.

I laughed when I read this. Sorry, I don't mean to be offensive, but I couldn't help but find it funny. Well, at least you were in Paris on your birthday, right?

Bateau le Calife dinner cruise. You won't be the only one celebrating a special occasion.

Take her to La Tour d'Argent for lunch and indicate it is birthday celebration on the reservation (reserve as far out as possible, I think it is 3 mos -- we did that and got the best table in the house)
https://janettravels.wordpress.com/2016/03/01/anniversary-lunch-at-la-tour-dargent/

La Tour d'Argent is indeed one of Paris's most famous restaurants. But if I'm reading the online menu correctly, the prix-fixe lunch is €105 per person. (That's FAR cheaper than the a la carte dinner options, or the prix-fixe dinners). If you have that kind of budget, go for it!

https://www.tourdargent.com/restaurant/menus/autour-du-dejeuner

In fall of 2015 the menu at La Tour d'Argent was 85 Euro so it has gone up. That is not a very expensive menu (at 105) for a celebratory multi course lunch at a Michelin starred restaurant, but one can certainly find cheaper and very nice meals. We rarely splurge on something this pricey.

Les Ombres which is also spectacular still has relatively cheap menus.

That depends on your daughter's interests. Almost completely. Some people would be mesmerized and deeply moved by a visit to Père Lachaise cemetery. Others might find it boring or even creepy.
Some might want the splendor and attention that comes from a visit to a Michelen-starred restaurant. Others might find a more memorable night at a simpler Parisian restaurant or bar, where one can feel as if they're a part of that magnificent city.

If you go shopping while you're there keep an eye out for what she likes or wants. Find a reason to slip back by yourself to get it. It might be a chance to get gifts for both of your daughters.

Have a nice dinner. Get tickets in advance for an evening visit to the Eiffel Tower. Stop by the champagne bar up top for a glass of champagne. I think the official drinking age is 18 in France so your younger daughter may be out of luck.

Does she like cooking? The market cooking class at https://cooknwithclass.com/paris/ is a lot of fun. I've taken 4 or 5 classes over the years there and have enjoyed them all. In the market class, they take you around to various shops in the local market and talk about the various products and buy the ingredients for dinner. You then return to the school and prepare dinner under the guidance of the chef. They are a bit pricy, but you get a very good meal and they are really fun if you like food. It would be fun for the whole family and if someone does not like cooking, they allow a guest to join for dinner for a lower price.

You could also get a really beautiful dessert at a pastisserie shop. Pierre Herme which has wonderful macarons and pastries.