What's the proper way to request greek ahead of time?  It it appropriate to use the term "greek" or "pse" in the initial e-mail contact?

You're better off using the term "Greek" instead of "PSE".Just ask her if she allows Greek.

In your initial email I would say something like "I saw your ad on www.whatever.com   I really like greek and would love to schedule an appointment with you..

Also if you stick to TER reviewed providers, read some reviews and see if Greek is on the menu.

Well if your a VIP you can see it in her reviews. I
would not ask it in an email. The providers I know
will not answer it. Best to ask in person. Greek is
a vary personal act.

and sometimes a provider can be put off by candidly asking for Greek in an e-mail.

I often make a metaphor to vacation travel when I e-mail a provider by mentioning my predilection to Greek culture or the beauty of the city of Athens and how I always try to include it in my travels. This way an adroit provider can either answer in an affirmative agreement or politely side step it by saying they have never or have no interest in that vacation spot.

You could say that you wood like to climb the Acropolis, or you could ask if there is an additional admission fee to tour the Parthenon.

Thank You

Get a TER vip account and check the providers profile. Also check the ad and read the reviews. If the provider is a provider who requires references sometimes it help to use a reference from a provider that you did greek with. That works out good because provider that you are seeing will be prepared.

Some providers want you to be a regular before they give you greek. They want to size you up to make sure you are not to thick for them.

...in the email process, most providers who do provide greek reserve the right to offer it or not offer it upon meeting you and "seeing" you.  As others have said, stick to well-reviewed ladies who "offer it".  When you are with them, then you can ask them directly if they don't bring it up themselves.