Well, well, well. You could understand her behavior as another adult because, seriously, raising a child could be very hectic. Just think about how much that little brat tormented her on daily basis for years on end. But, on the other hand, from that child's perspective, there is no difference between pretending to abandon her and actually abandoning her—at least until her mother comes back. That's the point of threatening. It's one of those. The good old practices. Most parents won't do something like this anymore because it's unhealthy. But I'm pretty sure a lot of you guys experienced something like this as a child. I was repeatedly told that I'm not my parents' child when I was a child. And I didn't even do anything to upset them. They giggled as they watched my reaction.
If you're gonna have a child, then don't do something like this. And treat this chapter as a work of fiction. No child got almost abandoned in the making of this manga.