Gummy bears, cookies, etc. that contain marijuana usually taste slightly different than their regular, non-laced counterparts so I'm not sure it would have been easier. An 11 year old surely would have questioned a "weird" taste. Also there aren't really any dispensaries in Colorado Springs so she would have had to have gotten any of that elsewhere. Trust me. I live in Colorado and have extensive knowledge of this industry, not through personal use but through business.
Also keep in mind, no one really overdoses on marijuana. If she gave him a large dose, he would have probably just gone to sleep. It wouldn't kill him, even in the extreme.