My 3 year old daughter is addicted to watching cartoons/ toddler programs on YouTube. She's gained the intelligence to even unlock my phone and remembers my passcode very well. How do I get her to lose interest? I usually give in to her during meal times as I want her to finish the food.

You have to make sure she kicked off this bad habit which you have made her nurtured. Take things slowly so that it will not cause backfire. Alternatively, you can change it from Youtube to others like providing her with a reward system. This will enables her to finishes her food in a shorter time and you share the knowledge that there is always alternatives available. Taking this opportunity to share with her the pros and cons too.