Can I use a mental illness in a book without sounding like an after school special?

Good morning!

So, following the rule that a writer writes, I've started a new writing project hot on the heals of my most recent release A Hero's Spark.  This time around I'm working on a series, an actual series, one that's linked by the exact same character doing what she does.  And it's going to be an inspirational series, so no swearing, no sex, so basically you won't have to hide it from your kids, but hopefully it'll be entertaining.

As I started writing, because I'm not an outliner, I just sort of go with the flow when it comes to writing, I was also watching pretty much everything the Discovery Fit and Health channel was showing during their "Psych Week."  (Think "Shark Week" only instead of man eating sharks you've got the entire spectrum of mental illness and psychological quirks.  It's awesome.)

As plowed through a couple pages of character development, an idea crept into my typing. (I'm going to sort of use the "Adam and Eve" defense:  It wasn't me, Lord, it was the fingers you gave me that wrote this.  LOL!)  And, the more I typed, the more I realized that I'd found an interesting character quality for my character, Nora Hill, to have.  And I have Psych Week to thank for it.

Here's the thing, though, I'm worried about:  Can I write this without sounding like some schmalzy, do gooder, after school special?  

Like most people, mental illness has touched my life in many different ways, some very close to home.  I, personally, have not been diagnosed with a mental illness...yet.  (I have my suspicions.  As they say, "Insanity runs in my family.")  So can I, in good conscience and without sounding smug or condescending?  

I very much want this character to be real, but also to be very memorable.  I fell in love with all the Stieg Larsson books and with the one US film.  Rooney Mara is so perfect as Lisbeth Salander it takes my breath away.  And the thing about the character Lisbeth is that you know, YOU KNOW that girl isn't completely right in the way the world thinks of people being "completely right."  And yet, she strikes a chord with me, with millions of readers because in spite of all her "flaws"  (based on society's ideals) she is a hero.  No one, after reading those books, is going to forget Lisbeth Salander. 

We're also getting into that old rule, "Write what you know."  While I do believe you should know what you're writing, I think if all authors stick to this rule we'd be missing whole huge chunks of literature and awesome, awesome reading.  I mean, I'm pretty sure James Patterson has never met winged teen agers, and yet you cannot deny the appeal of his Maximum Ride series.  (Teens and adults alike are going to love those books.)  And while Charlotte Bronte, I'm sure, knew what it was to be a governess, I doubt very much she'd met a lord who kept his insane wife locked in the attic.  (Oh, what, a spoiler?  for "Jane Eyre?")  If I follow that rule, I'll be relegated to writing stories about Midwest Suburban while girl life.  Yawn.

So we're back to the question, am I able to write someone who is living with a mental illness?  Should I even try?  Will anyone want to read it when I'm done?

I guess we'll find out.