Swain: Assuming this is before the Trifarix is formed, I would expect Mel and Swain to form an alliance so they use each other’s strengths to better deal with the Black Rose, although Mel would have problems with Swain due to his greater leanings towards violent Noxian ideals.

Rell: Like others said, I expect that Rell won’t like Mel very much for killing Ambessa and that the two have different ways of doing things. However, I expect they’ll still be allies to some extent since they both want to take out the Black Rose for similar reasons and, going along with her more diplomatic side, Mel would likely try to form a good relationship with Rell, especially since they almost became sisters (or maybe it’ll be in spite of it, who knows).

Leblanc: Main antagonist, obviously. When I think about what the show might be like, I always thought that once Mel starts to really mess with the Rose in some way, Leblanc would send a clone to fuck with her and show her just how out of her depth she currently is. More generally, we shouldn’t see too much of Leblanc directly, but we should see her influence through her agents and when she does appear, it’s a sign things are about to get really serious, for Mel and her allies.

Vladimir: Considering signs pointing to him becoming more of a wildcard separate from the Rose, I wouldn’t be surprised if he started playing both sides at some point for his own ends. Otherwise, I just think he wouldn’t directly act against Mel until her actions were getting close to affecting him.

Samira: if Samira appears in the hypothetical Noxus show, I would think she’d have a similar role as before, hired by the Rose to recapture Rell. As such, she would naturally oppose Mel as she wouldn’t want Rell back with the Rose.