I would think Napolitano would understand the defintion of burglary better:
To illegally enter a building to commit a crime, usually theft
Also, typically to gain a conviction the prosecution needs to be prove criminal intent at the time of entry. Ryder entered the store legally, so the prosecutors probably tried to prove that she went to the store with the intent to shoplift, a rather difficult allegation to prove beyond a reasonable doubt unless the perp doing something such as wearing a coat designed for shoplifting.
Good analysis, but remember she had shopping bags and tissue paper to wrap her purloined goods, and also a plastic garment bag. I would think that the burglary charge would be pretty easy to prove.