To PM here click her name on left <--- and it'll bring up a new screen
where it'll have a button that says "PM" click it type in subject and your message click submit and it'll send it to her.
Then she'll see a notice she has a new one when she logs in at top of the page.
To check your PM's look up top and see where it says "Private Messages" Click that and it'll take you to your inbox. (It'll show "new message" if you have any new ones)