I know people don't like to acknowledge Zoro's true strength. Let's be real. If Law and Kid wants to fight title so bad, like so many claim, who's going to take on Big Mom. The obvious answer is Zoro. He going to do it all.
I would not be surprised, if BM would not try to defeat SH. She could just wait for the outcome of Kaido's battles. If he won, but he is severely wounded or exhausted, she could finish him off. If Luffy and others are on their last breath, she could easily take them down. Big Mom is the real threat now.