In the vast majority of cases the truth is by far the best route to take. I suggest you tell your daughter in a non-accusatory way that you found the candy in her room and that you know that she took it. We are taught to be honest by the Torah verse, “Distance yourself from falsehood” (Exodus 23:1). Or as people say nowadays, “honesty is the best policy”.
Then you can ask her to try and explain why she felt she had to lie about it. If it is approached the right way I would hope that your daughter will learn a very important life lesson without it being traumatic. I am concerned that if it is dealt with too harshly that there is a chance that she will simply learn that she needs to be more careful next time she takes something that she shouldn't have.
May you be blessed with immeasurable happiness from your daughter!
Reply from the mother:
Thank you. I greatly appreciate that you took time to help me with this situation. I spoke to my daughter calmly and pray that she does not ever feel that she needs to lie to us. I emphasized how much I love her no matter what and I am more sympathetic to the truth. I will let her know she can always come to me and she seemed relieved and pleased.
Reply from the Rabbi:
I am so happy to hear that she was receptive and that, hopefully, it has strengthened your relationship.