Big Mom, what a monster indeed. But also a lot of false bravado to uphold her reputation. If people don't fear her, her soul pocus won't work. She will get weaker and Tottoland will soon be overrun by thousands of pirates giving the Marines a great chance to take her down while weakened. That's why she followed Luffy as well as a bit of hurt pride.
Big Moms act of bravado against Kidd and Law is kind of like when Whitebeard lied and said he sent Ace after Blackbeard. He knew that his entire empire without that fear of "never touch a WB-affiliate" would crumble in days. And so it did after the war.
So now with Big Mom humbled yet again will we see Tottoland in tatters? Katakuri is there, sure, but he can't take on large armies by himself. And surely Blackbeard is going there to take the Road Poneglyph anyways.