Add me to the crowd that doesn't see you as having done wrong. You could either have tried talking her into letting go of her sister who she was hurting, or you could smack enough shock into her to get her to let go. Desperate times call for desperate measures. She knew not to do what she was doing, and she was hurting another child.
Spanked dd yesterday for first time... :( Looking for alternatives, Please don't judge - Page 2
I don't think it was wrong either. And I don't think it called for an apology on your part, but rather on hers! in fact while I am generally not a fan of forced apologies a la Supernanny, whenever ds hurts dd (mostly accidentally through carelessness) I insist that he tell her "sorry" and give her a hug. I used to think that insisting on an apology would be fake and teach him to lie as many people here will say, but on the contrary I ahve found that he now will often say sorry and be genuinely empathetic to her, overwhelming her with hugs and kisses, without me even prompting him. So in your dd's case, I would have had her apologize to her sister. Even though they are babies, they also deserve respect and consideration as little people! And I know if someone did that to me, I'd want some sort of apology or hug or something! Certainly as adults we are expected to show basic courtesy and manners to others, and we are raising our children to function in the world. So I don't feel that we have to tiptoe around them all the time for fear of hurting of their feelings or upsetting them. Even if your dd WAS upset by the "spank" it was a natural, imo reasonable/instinctive consequence to her actions. My opinions would be very different if you had snatched her up, grabbed a belt and beat the daylights out of her. What you did makes sense in light of the circumstances.
I second the suggestions of a bear hug. We do this with ds when he gets out of control and it is very effective.
If she seems very hungry you could try filling a sports bottle or carry-around cup with a nutritious fruit smoothie. That is pretty filling and might help with her moods!
Just to make you feel better, one time ds in a fit of sensory overload suddenly came out of nowhere and bit DP's leg right down to the white meat. DP freaked from the shock (he was apparently reading and totally engrossed) and smacked ds, who was not expecting the smack and went flying "across the room." I'm not sure how accurate the "across the room" part is, but they were both rather shellshocked when I came home from work, and they both felt equally bad! The point is, things happen, we get caught off guard, and it's ok.