All behaviors can be understood as strategies to meet needs. Needs exist on all sorts of levels; physical, emotional, spiritual; and some are immediate and urgent (like oxygen) while others are less so (like friendship). But all needs are legitimate. Some needs are easy to identify (like hunger and rest), and some are subtle and elusive (like love or security or privacy). And all needs are legitimate, though of course some appear more so than others.
So, looking at your problem objectively, it appears that your daughter's behavior of eating more than you think she needs, and even "stealing" food in her own home, is an attempt to meet needs that perhaps she can't even identify and understand. Before you do anything else, please talk to her pediatrician and be sure she doesn't have a metabolic disorder. Some serious illnesses (like diabetes) have hunger as a symptom.
And if this has been an issue in your family for more than a few weeks, I'd guess that your daughter is struggling with other emotional problems brought on by the issue itself. Self-esteem, insecurity, anger, disempowerment, resentment and fear all have a huge impact on many people's desire to eat either more or less than "normal."
I'm so glad you're asking this question, S.. It's a brave and loving thing to be so honest with all us mothers out here. The emotional urgency, frustration and anger you describe suggests to me that you may have some unresolved food or body image issues of your own, and it is all too possible to project our own stuff onto our children without ever guessing that this is happening. (In fact, it probably occurs to some degree in every parent/child relationship.)
May I tenderly suggest that you get some counseling with your daughter? My hope would be that she have a trained advocate who can gently help both of you to identify and describe what's driving her eating if it's not primarily metabolic. If this doesn't happen soon, I know from personal experience that she could end up with emotionally and physically damaging issues around food for the rest of her life.