I would tend to agree with you, but what if the parents did stick her but took blood instead to test and see if she was getting injections of some sort???
People on feeding tubes are often tested for glucose levels. Its not all that easy for someone to just walk in take a blood sample and have nobody notice that you are doing that,not to mention if you don't know what you are doing your not likely to get the blood period.
Insulin is given subcutaneously, our just under the skin ~~ a blood sample is taken from a vein. The puncture marks were on the skin, and not a vein, according to my understanding from the article.