When I say to someone can I drop something off I mean just that, I go to their door and drop it off, not expecting to be asked in, whether it is my family or not. Many a time I have dropped something off to my family and not seen one of them for more than 2 minutes. If you had wanted a visit, you should've ask for that in advance. As others have said, they might have been going out, had visitors, doing jobs or 100s of other reasons, why it was not convenient at that very time.
Whatever the reason your DIL obviously did not want you inside, for reasons known only to herself (possibly you too) but we cannot comment on that. It does appear rude yes, but appearances do not always tell the full story.