So I've always thought that Big Mom never ate Carmel, but that Carmel used a technique to sacrifice her own life, turn into soul form, and physically possess and take control of Linlin's body. The Immortality Surgery isn't the only life sacrificing secret technique known to devil fruits. Princess Mansherry had one too that could restore buildings and islands and not just people, it was just never used. I think it's super likely that instead of cannibalism, cipher pol appeared to try and murder Carmel and steal the kids, but Carmel possessed big mom and drove them off somehow. The giant who witnessed everything could have been disgusted because he watched Carmel reveal herself as a human trafficker to the world government and Streusen could have been laughing just because he thought it was funny to see a possessed Linlin beat up a bunch of grown government men.
Now that the Harald plotline is happening I'm kind of back to this theory. What if the reason Harald seemingly changed his position is because of the giant from Elbaf who witnessed Carmel selling children to the government? He reported back to Elbaf about what was really going on and it changed their culture.