Why would the return not be a concern? She would need some for/during/after the flight, wouldn't she, especially due to the nature of these lenses?

Did you ever ask at an optician, or check the American pharmacy in Paris? I wore Boston lenses for almost 10 years, and I didn't have an issue finding solution in many places around the world where I lived or worked. (Worst case you can always order online on a European site and have it delivered to you, or pick it up along the way)

But I take it that you are taking checked bags, and this smaller bottle is just for the flight. CDG is generally polite but very firm about keeping to the rules. Having said that, I would just put it in your regular liquid bag.

Edited to ask: Can she use the one step Simplus solution from Boston (Protein remover and wetting solution in one)? It comes in a 2oz travel size. http://www.bausch.com/en/Our-Product...ng-Travel-Soon