Let's say she doesn't run away
How does she lose to Kid and Law ? The child does not have an advanced haki The law has no advanced haki Unlike Luffy, Oda doesn't give them powers after multiple rounds like Luffy does against Kaido.
They never expressed a wish to beat Big Mom.
The only one who said it is Luffy in chapters: 651 696 871 and probably a chapter I forgot.
What Kid fans don't understand is that Big Mom appears to be preserved in Erbaf, the Isle of Giants where she grew up.
There are connections with Loki, Lola, Ussop and many other things. Big Mom in chapter 998 or 999 told Kaido about the road poneglyphs, she came to Wano for her own sake and left. Besides, she told Perospero her first son who did not want an alliance to trust him. Do you think it's by chance that as if by chance there is only Perospero fighting and beating Smoothie?
Luckily, would Big Mom's boat ever reach Wano? Big Mom is going to run away with her kids, surely there will be an emergency call or something.