That's a lot of languages! Try this website - http://how-to-learn-any-language.com/e/index.html - it has a language learning guide (including estimated study hours to basic fluency) and a good forum. You could also try All Japanese All the Time. Its an immersion method for any language (not just Japanese) that can be done without leaving the country :) ! Start with the "Table of Contents" (at the top of the page).
For French, have her do some reading in French, possibly with a French Audio-Book so she can hear and see the language. Maybe a French email or pen-pal? You could try having her listen to the French FSI courses. (They cover several languages and are public domain, created by the US government for training diplomats. They are being made available slowly at http://www.fsi-language-courses.com/). They don't slow down the language so she can test her listening comprehension and there is a text so you can preview what she will be learning. It's not (to me at least) a user-friendly course, so I am putting it off until I hit the intermediate level.
How many she does at the same time depends on how much time she has, but continueing her Latin and French while starting a 3rd language would probably work. After she has the basics of the 3rd language she could start another one. The good news is she is old enough for adult level material, which gives you a lot more options.
I love languages, currently I'm working on Ancient Greek and Spanish! Best of luck to your daughter.
Amy