When my child hits someone, should I always make her say she's sorry?
It can be very hard to say "I'm sorry." It's harder still if you don't mean it! We certainly want our children to learn to feel remorse and be truly sorry for their actions. However, apologies should come from the heart and be said only when meant.
When your child swats a friend, takes snacks without asking or grabs a toy out of another child's hands, she is not sorry! What she did was wrong, but she is usually not sorry!
Insisting that children apologize when they are not actually sorry is teaching them to lie about their feelings. If children are encouraged to apologize when they do not mean it, then "I'm sorry" becomes meaningless to them. It's just something to say when they've done something wrong, and it generally gets them out of trouble.
So here's my advice: Teach your children to take responsibility for their actions. Teach them to admit that they made a poor decision, broke a rule or did something they should not have done. Teach them to speak the truth: "It was wrong of me to hit," "I shouldn't have taken the candy," etc. are acknowledgments of misbehavior. And a lot more truthful than telling your sister you're sorry (with fingers crossed behind your back!).