You should tell the providers that you have met that they may be receiving a call from the one making the request. The provider who is screening you will want to initiate the call and may want to check out the girl beforehand to be sure she is legit and reputable. If the call came to her the way you describe, for all she'd know it could be a fake that you had set up.

However, your reference likely will appreciate you giving her a heads up, so you've got the right idea. And yes, most providers are fine with it, but you must get her permission first.

Have a few details ready. . .

if it has been a little while since you have seen your provider that is giving the reference, make sure you have a couple details ready to jog their memory. This will make it easier for the provider trying to get the reference. For instance, the provider then might call your reference and say "Hi Sheila, you saw John back in December -  he saw you when you were staying at the 4 Seasons. You had just been shopping and bought a Gucci Bag". Something silly to jog memories.

Good luck!

Summer