The Mechanics of Writing - An error I frequently make

I recently heard back from my editor regarding a mechanical error that I repeatedly made in Eagle River. So, I am posting her correction here for other writers and to remind myself (Thanks, Nancy!)

Is this right?
Why didn’t they just drive off with the stash once it was in their possession? She asked herself.

Or is this right:

Why didn’t they just drive off with the stash once it was in their possession? she asked herself.

(if you said the second one you're right!) I see this over and over again where an author capitalizes the first letter of the tag (She) when it should be lower case. Many seem to think the question mark is the end of the sentence when it's not. This is an entire sentence, hence why she needs to be lower case. It's the same with a sentence that ends with a comma before the tag.
Example:
(Correct) "I am going to the store," she said.
(Incorrect) "I am going to the store." She said.