Make sure she is VIP, or otherwise your effort is in vain.

Assuming you know she is VIP and you know her TER handle, simply go to "Mail" and then "Compose" and then enter her TER handle.

Alternatively, go to her TER review page, and see if there is an option to "Send Private Mail to Provider" or something like that.  It's located near the top of her review.  If you don't see that, she can't get PMs.