One thing we've all been warned against is the TSTL heroine. (Too Stupid to Live, should you not be up to speed on all the acronyms.) This is the heroine who goes down into the dark basement to see what the noise is—when she's aware there's a killer in the neighborhood. How to avoid this syndrome has been discussed at length, and I'm not going into it again today. Instead, I thought we'd look at the perfect heroine.
Back in my early writing days, when I was learning the craft via fan fiction, there was a great deal of discussion about not creating a Mary Sue. In fact, there was even a test to make sure you didn't have one of these unbelievable heroines (or, in fact, any character) in your books.
Is this to say that you can't have a heroine who is fully competent? Of course not. But you can't just plop those convenient skills in front of the reader when it becomes convenient for her to have them.