Board Thread:General Discussion/@comment-24589671-20141208022047/@comment-24674051-20141212141344

True, but Ingrid did not give Regina any reason to go that far. She appeared 18 years into the curse, so it caught Regina by surprise, but I kinda got the impression that she had been around a couple of days before Regina stumbled upon her. Enough to get the lay of the land, and blend into the background.

Regina likely had Sidney keep an eye on her for a few days, and when nothing else suspicious happened, she dismissed it as an oversight. Ingrid was smart/clever enough to know when to lay low.