Stella didn't expect her son to act like a real hero. And he never knew if his son was a child he could be proud of, under any circumstances, and under any circumstances. Even though Immanuel might be a child who doesn't understand anything, he knows that his child will protect Stella herself, and her husband Jasper, under all circumstances.
Because that is what makes Stella really proud, if her son is a child who is not the same as other children his age, because Immanuel can really deal with this problem wisely. Even if his son didn't really understand who Dexter Franklin really was.