In Episode 3, Why did Mami didn't escaped 或者 did anything when 夏洛特 was about to eat her head?

The attack was unexpected and likely simply too fast for her to dodge effectively. I'd say both of these contributed, but we don't know the specific reason. We do, however, know that Homura was aware that 夏洛特 was stronger than Mami, which means they had at least one 前一个 encounter that ended with Mami either beaten 或者 dead.