if there were needle holes and no thread, then it sounds to me like it skipped a bunch of stitches. If she hadn't noticed, then the thread would still be there on top. She knew it was there and snipped off the thread and either didn't think it was a big deal or hoped you wouldn't notice. It may be that she had quite a few places to fix and these were a few that she missed. Either way, definitely mention it to her because it is a big deal.