Okay. ""Chick Lit" is a genre of writing also known as 'women's fiction' and books that I absolutely love.
Why?
Because the really good ones are all about life, the way it is, warts and all.
The're not JUST  "romance books" as some people believe, although there's usually some kind of romance in the story.
I  personally think they're 'journey' stories, where the heroine moves from one point in her life to another- hopefully better- place and shares all the tragedy, giggles,fun with friends, romance, and evolving she does along the way.
They're about hairy legs, muffin tops, the eternal search for the perfect hairdresser, best friends, boyfriends, your mental family, his mental family,and on and on it goes. They're really about transformation; from caterpillar to butterfly , or sometimes they're about transformation from scared caterpillar with low self esteem to smart, sassy self confident caterpillar who makes the butterflies green with envy!
My personal favourite Chick lit books have a healthy dose of humour, because life is often funny as well as sad or stressful- and often at exactly the same time.
 So,Young Adult or Teenage Chick Lit is- books about the same stuff for a different age group.
I'd even go so far as to say that the "Letterbook Series"- Both "Amy's Secret" and "Passion For Fashion" is Tweenage Chick Lit. All the main characters in both books are on a journey that deals with life, for them it's school, families, best friends, boys and just getting through the day.
Sounds just like Chick Lit to me!