I just signed up for TER and have scheduled an appointment with a provider this week.
I am terrified of getting busted by LE (though this person has reviews going back for a couple of years
and the phone number google search did not turn up anything suspicious).

hobbyists, then you should be fine.

What is her TER ID?

There's no need to worry if the lady is well reviewed, or go with an agency that has been around a long time.
Look at the ladies reviews and make sure the guys that reviewed her are also well established and have loads of reviews under that name. There are many guys on here that have over 100 reviews, just like Keystone which means he has been around for a long time.

It sounds like you've done your research and should be fine for your first foray into this playground.  

You don't have to use your cc for your VIP membership with TER.  Check out the payment options and you will see there are quite a few.    They make it pretty easy to join and not have to use personal information.

They even have your cc information. The third party hopefully has enough security and separation of payment. I am pretty sure the payment is billed different company name as well.  
         But yes you could use prepaid cards ect.

I paid via a gift card which I bought with cash at the store.