Writing Wednesday: When Characters Invade

About a month ago, I sat down to write a certain scene in my WIP. I had it all planned out it my head, where it would go, what would happen. And then Hailey showed up. She wasn't even a blip on my radar until she started flowing from my fingers. Now, she's become such a favorite character of mine--and a huge part of the story as well--that I've had to go back and fill in other scenes where she shows up.

This was the first time I've had the experience of a character invasion. I was a little annoyed at first. I mean, why couldn't my characters behave like I wanted them to? Slowly, I came to realize that this was for the best. The story was missing something, someone to help the MC grow. It just happens that maybe Hailey pushed her way into the story for that reason.

Now, I'm excited to write more with her in it. I'm also a little scared that I've been neglecting my other characters, or maybe they are all in hiding at the moment. None of them seem to be pecking at my head much.

Seeing as this is the second fiction piece I've started in my adult life (the other being on hold because of some major plot issues), most all experiences I have are new. I expect many writers have this happen. If you're a writer, have you had this happen to you? If so, how did you handle it? Did you ignore the character or let him/her flow to life on the page? How did it change your story?

Note: If you're a non-writer friend reading this, I may sound a little insane. I mean, characters talking to my in my head? Well, if you know me, you already know I'm insane and this shouldn't bother you, right?!?! No, really. Apparently, this all perfectly normal, or so all my writer friends who also have characters talking to them tell me. ;-)