Going to assume she is already very familiar with WDW, so I would try to guide her to the things that are either completely different in DLP or at the very least have enough changes to make them interesting.
However, the first rule and in my opinion most important one is to try and visit on a weekday. DLP is very popular with locals at the weekend and so you can get so much more done on a weekday. It will also be a lot busier during the French school summer holidays (which this year are 8th July to 31st August), but she might not have that option given she's studying as well, so is probably tied to the same dates.
If she only has one day, I personally would ignore the Walt Disney Studios park and focus totally on
Disneyland Park only. Until the Avengers Campus opens later in the year, there's really only Crush's Coaster in the Studios that is truly unique (now that Remy is also in Epcot) and the queues for that can get horrendous, so the main park is the way to go.
The ride to head straight for is definitely Big Thunder Mountain - the version at DLP is the best out of any of the Disney parks and takes place on the island in the middle of the lagoon in Frontierland. Similarily (Hyper)Space Mountain is also a lot different as it is a proper high-speed rollercoaster with inversions and video effects, but that does depend on her tolerance for thrills. Indiana Jones is another rollercoaster with an inversion but isn't amazing and over very quickly, so I'd only do this if the queues were short. Phantom Manor (e.g. Haunted Mansion), Pirates of the Carribean and Small World are kind of similar to the US versions, but are still different enough to be well worth a go.
Star Tours is the same upgraded one that's in WDW but with some dialogue in French, while Peter Pan, Mickey's Philharmagic and Buzz Lightyear are virtually the same, so skip unless those are attractions she really enjoys. Autopia is more like the one in California than the Speedway at WDW and has multiple routes depending on which lane you get allocated, but the queues times for this can vary massively - seen it with both really short and really long waits and can never explain why. Obviously there's loads of kiddies rides in Fantasyland, some of which are ones that have been removed in other parks, so it's a possibility she may find something she used to love is still there in Paris (Snow White, Pinocchio, Dumbo, Casey Jr, Storybook Land Boats, etc.)
It's also a lovely park just to wander around - incredibly pretty and full of hidden gems and shortcuts (most of which were designed to be under cover, so you could get from one area of the park to another staying dry if it is raining, which is obviously something that happens much more frequently than in Florida!). Don't miss the Liberty and Discovery Arcades, which act as indoor bypasses for Main Street but also have some lovely artwork on the walls, and the Castle itself which features a dungeon with an animatronic dragon and well as an upstairs area with stained glass windows telling the story of Sleeping Beauty and a balcony overlooking Fantasyland (assuming this is still open, not sure myself).
Finally, don't expect too much from the food. The counter service stuff is fairly bland (but not terrible for theme park fast food) and sit down meals take a LONG time - would steer clear of these with only one day at her disposal.
