My experience has been that if you wanna use the stuff, do it beforehand and tell her that you might enjoy a little before.

It doesn't put her in the position of disclosing whether she enjoys it or not, and she can always say, "Please don't show up stoned."

If providers are touring and they don't have a connection but like the 420, chances are pretty good that they will tell you to bring it along if you want and then partake if they so wish.

That's been my experience.  But most providers probably don't want to do it until the end of the night when they don't have more appointments, and almost all of them don't want it publicized that they are cool with it.

In NYC, it's more difficult to do it in a hotel room, anyway, because of the non-smoking laws.