I think, if you really are a close friend. You should tell her the truth, what you think about her lazyness. Not right out loud.
But like. 'Hint'.
Tell her (in a very friendly way) that you expect both to work hard. If she is lazy, try to organize the work between you two. And like, encourage her to do a good work and stop slacking. You will help her this way and it should also make it easier to work together in the future.