How much daily $ for a teen in Paris

If she doesn't have luxurious tastes I would say that 50€ per day is enough to participate in the purchase of basic food and drink for the meals taken in the apartment + some possible outings to restaurants or bars + bus/metro tickets in Paris + some museum visits or tourist site
This does not include any visits and expenses in clothing or fashion shops in general or souvenirs/gifts brought back for mum and dad and friends
It also does not include unforeseen expenses which by definition cannot be foreseen.

Consider to have your teen work backwards. What do she and her friend plan to do? What does it cost? The internet can provide all information: admission fees, metro prices, menus, shopping at Monoprix, etc. Add some for souvenirs, treating the friend to a meal or two or another activity for hosting her, and some "mad" money, done!

Assuming you mean two full weeks (14 days) I'd send her with €100 in cash and a debit card that accesses an account with the equivalent of 1,300€ in it. If she is as you describe, she should still have money in the account when she returns but if she has a minor emergency or wants to buy souvenirs, she has a some extra cash.

The museum/attraction cost is easy enough to budget. I am sure your daughter has things she wants to see and the friend has things she wants to show her. Go ahead and make a list of those items now and you will know roughly what that cost will be. Does the friend have a car/scooter or will they be needing transport? You can budget 2 weeks with a navigo pass plus some extra for cabs when the metro is not practical. The biggest variable will be food. I agree with the other posters that 50-75 a day seems like a good range. If it were my daughter, I would want her to have a credit card backup for emergency expenses. Just lay out your expectations ahead of time and if she is mature enough to fly to Europe alone then she should be able to live within the budget or be able to explain to you the need for any overages.

Thanks for all your thoughts everyone. While we like the idea of budgeting by creating a full plan for the visit in principle, departure is in two days (yes, sudden .... we got the tickets yesterday, but they were quite a bit cheaper if she left right away) Because of the short time frame, we will send her with a fixed amount that should cover most everything, and a credit card as emergency backup. Sounds like 75E/day should be enough to have a great time, and she can take any extra off to college with her in September.

I say €100 per day. Lunch and dinner out can easily be €40-€50. There are métro tickets, museums, souvenirs, and the occasional bar drink or just a café stop in the afternoon… AND don’t forget pastries and Berthillon ice cream which should not be missed.

hey hey ollie
i agree with JHK. put $1100 on a debit card and have a great time. i would not want to be carrying that much cash on person. seen too much ugliness with either pickpockets, dropping out of pocket and once it's gone it's gone.
if worse comes to worse you could have added to account from your end.
she'll go have a great trip, have a friend to show her lots of people, places and things. go to outdoor markets, but things for dinner and lunch, don't forget the fresh bread, the desserts.
last trip in oct 2019 i was on a mission. who and where made the best eclairs, forget where but at la deux maggot in the 6th was 20E ouch. 2 years before was my mission of french onion soup and best to me was up montmarte at la maison rose
went to angelina's for fabulous hot chocolate and breakfast, had crepes all over, souffles at la cuisine de philippe in the 6th behind luxembourg gardens, celebrated with champagne (bring glasses plastic if need be) watching the blinking lights at eiffel tower, walking to the "i love you" wall and taking pictures
i know your daughter is young but we had my friends daughter that had a great time with us "old ladies" LOL enjoy
aloha

I must be a bit more conservative with my money...and I did help my daughter with deals like this one. However, 100 Euros per day for an 18 year old is way over my comfort level. There's a lot of trouble that might brew for that amount of money. You know your daughter, you think, but her friend and her friend's friends will be a draw. Eighteen year olds in Europe might be perfect, but so many are not, regardless of what we as parents think. LOL. At that age, picnics, breakfast at home, and many easy suppers at home fit the bill. There will be wine, patisseries, etc. Walking Paris is quite inexpensive. You just want to tease her with this trip. She can return as an adult when she has money to splurge on the expensive things.

At 18, she must have a bank account and debit card, just add the full amount you decide on into that account. You can always add more to her account, but I'd be more apt to provide 50 or 70 Euros. Some days will be super cheap and some will be more, just like when we all travel. If you are worried she might have an emergency, send her with a credit card as well. My daughter, even when under 18, always had a credit card for emergencies on one of my accounts...so I would see the bill.

I moved to Paris on my own and by myself when i was 18 yrs old, lived there for a year. Found myself a job and a place to live. I had very little money and had to budget very carefully just to afford a museum/site and 2 métro tickets each day…i never had enough extra even for a pastry. Lived on a baguette and Boursin cheese for dinner most nights, lol. So i do know how frugal one can be in Paris. I got the impression this was a gift to the OP’s daughter and it being a 2 wk vacation there, which is why i suggest €100 per day which will not be luxury even at that amount. OPs daughter can relax and enjoy herself, and buy that cute €40 Tshirt if she wants to, eat a €5 pastry every day, a €5 coffee and a €5 Berthillon ice cream, plus museums/sites and a bus or métro. But yeah a bit less works too if she’s good at budgeting.