[@Renny]
How about one of these two choices;
1. They see each other again, realize the other is still alive, perhaps a short warm reunion, but right after words the situation finally sets in and they realize they are on opposing sides. of course they would try to convince the other to come to their side, but that won't work. So, even though its something neither wants to do, for the better of the galaxy they fight.
2. Ben knows its Odette but Odette doesn't know its him, making her fight him not only for the better of the galaxy, but also as her own silent revenge thinking Kylo Ren killed Ben. And of course, Ben, not wanting Odette to know its him, fights back to defend himself.

What do you think? I personally think I favor the first one a little bit, but I'm open to either one XD Either way I think the part where they finally meet up again will be a lot of fun to write no matter how it happens.