Spaceflight Now has an article on the interest of European Space Agency managers of making a major contribution to NASA's Europa mission. What the article lacks is a statement of whether or not there is sufficient mass margin in the mission to carry both the newly mandated NASA Europa lander and a European contribution. It's possible that NASA doesn't yet know since it has been examining the lander concept, at the request of Congress, for only a few months.
If NASA concludes that there is mass for a European contribution, teams of scientists can propose concepts for the next ESA medium class mission selection. The competition will be tough with with other teams likely to propose a number of other compelling astrophysics and planetary mission concepts.