Well, it is possible, to put it simple you both will be working together almost as if you were working with a different person, be it a stranger, an assistant or working for someone else.
It is mostly thinking about what are you willing to leave to the other, what are you willing to do for the other, what are your strong points and what are hers. Its all about the agreement of what you both are doing, what feedback you provide to the other and well, if you can merge your styles first. And you can try, mix and match until you find what is comfortable for the two of you. Be it proportions, anatomy, coloring, inking, or if one does the characters while the other the backgrounds and so on. There is no specific guide for those things.
Some people sketch, and leave to the other the lineart, or coloring and such. If you have similar artstyles and even if its not the case, you can always grab each other's works and study them together, analyze them, recreate them be it by imitating the other's style or drawing on your own. What habits do each of you tend to have, what things do you repeat on drawings, what characteristics does each's styles have, etc.
