"You think about it."

When my third daughter was 3, I started to look for ways to have conversation with her without the other 2. In a group, any topic can be commented on quickly by older siblings so younger ones get left out. As I attempted to avoid that pitfall, I would separately ask her. What do you think about_____?" And she would look at me, not sure, like it was a trick, and she'd say, "You 'sink' about it Mommy."  We'd go through this several times until finally, she would venture an opinion or thought."  I did, this with her for a few years until she finally started answering the questions easily or sometimes would come to me and ask what I thought about something. 

The message: What she thought was important.  I wanted her opinion.

It was private, with no criticism or commentary by others. It's how you build their confidence in forming and voicing inner thoughts, which is crucial for success later on.

This is a tactic you can use with any age daughter. They don't talk to us because they fear our criticism. Opinions and thoughts are there in their teens and into their twenties. Good parenting practices don't stop just because they leave for college or get an apartment. Maturity is an inner state-of-being, not based on exterior milestones. When she reaches it, then and only then, can you be her "Friend."