I'm wondering about practicing with a person who isn't a native speaker.
Here, the main questions:
How do you work with a non-native English speaker to improve your abilities?
What questions do you usually ask from your non-native speaker partner to help yourself?
If they are of the same level you are, then perhaps you can agree upon a lesson you both are to learn in advance, and then during the exchange you review it together. You can also engage in conversation of course, to further improve.
If they are of a high level, then it should not matter they are not a native speaker, as the person above has pointed out.