Let's say you arrange a session with a provider well in advance, maybe a couple of weeks. And she says to email her about 3 days before the date to confirm and give a phone number, and that she will then get back to you with location. Having done that, when should you expect that she will re-contact you?

I've had some experiences where that happens a couple of days before the date and it reassures me that we're on. Other times I find myself the day before -- or maybe even the night before -- wondering if I'll be stood up. What's the norm out there? And at what point is it OK to reach out once more to make sure we're OK?

Most providers won't stand you up. If they have to cancel or move you, they'll let you know ahead of time.
It's usually the other way around; clients standing up providers or canceling.

I've had same day confirmations a few hours before.
And I've also texted a provider before leaving my house to make sure we're still on.

Since you booked a couple weeks in advance, keeping in contact is always nice since a lot of things can change in those few weeks.

Just a simple email saying something like this:

"Hi, I just wanted to confirm our appointment for today.  Please reply so that I know that we are on.  Looking forward to it!"

But don't bombard her with emails, texts, or calls.  She will not be happy.  As also mentioned, if she is a well-reviewed provider, chances are pretty slim that she will stand you up w/o good reason and w/o letting  you know she has to cancel.  In fact, this happened to me this week with a provider I have seen several times already.  She sent me an email telling me she had come down with a fever and felt it best not to see me.  She followed it up with another email telling me she was going to the doctor that afternoon, we were spsd to meet in the morning.  Yeah it was frustrating, but I got over it.

Swim

there is no set protocol..the norm is the night before..she lets you know the location and phone..you call five or ten minutes before to get her room number on an incall..this is for her protection and yours too..

But, if it makes you anxious, I'd rather that you contact me sooner than that you worry that I'll stand you up. It isn't a big deal - I wouldn't be annoyed by it at all.

If anything, hearing from you will make me more assured of your reliability.

I guess I'm a bit of a worrier. Hearing the night before makes perfect sense but I'm a lot more comfortable if I've heard back a day or two before and then it's fine with me if the lady wants ME to confirm the day of.

Morning appointments might need confirmation the day before.  If I have to travel a distance in the morning, I often call (again) when I am leaving...  with a Fav & flexible time, it gives her an ETA.  (Estimated Time of Arrival...  not a hobby term!  LOL!!)
HV

Evening before the date to reassure you.  She will would appreciate a confirmation for her the day of the date.  This is the reason many don't call to that day, I think it's inconsiderate, if they're so concerned they should call the day b4 and insist you call 2-3 hours before the date.