I've been working with Nala.
She does get a bit food/toy aggressive towards Simba. Not horribly, and she's never snapped, but she growls/ raises her lips. I've gotten to the point where she allows him to take a treat off of her paw. I'll continue working, but I'm not sure this has anything to do with what's going on with her and Duke.

It's the only problem i've seen from her though, she just wants to be alpha I guess.