I would say the correct answer is - she thinks that Higgins deserved it. Here is a quote from the text to prove it: <em>"And then you were surprised because she threw your slippers at you! I should have thrown the fire-irons at you." </em>You can see here that she wasn't mad or surprised she did it - it was to be expected.
Ponyboy realizes that Darry does care about him; Darry is strict because he loves Ponyboy and wants him to succeed. Ponyboy runs across the room and embraces his brother, thinking that everything will be fine once he gets home.