Ask her if she has a po box to send the gift to.

You gave her an envelope with cash in it. She fucked and sucked you, and you are still even.

Why not just book her again and forget about the mangina appreciation stuff. She's giving references because it makes good business sense for her to do so.

Re: Gifting a white-list referral

No gift required it is part of the deal to keep the community safe.

or the might think they are entitled to and expect gifts...

I learned a long time ago that any discussions on TER regarding tips and gifts is pointless. There are many hobbyists who treat this forum as a substitute for dating. They want to create a real girlfriend experience and as such like to bring gifts (flowers/candy/perfume, etc.) and perhaps take the lady out for the evening (dinner, a show, a sporting event, etc.). In addition, there are many hobbyists who feel that ladies are entitled to cash above and beyond their donations. It's there way of saying an extra thank you. But also keep in mind that these men may be in a financial position to do so. An extra $200 tip may be the equivalent to $20 to another hobbyist so keep that in mind as you read posts from So  hobbyists that tell you they always tip or bring a gift.  

Conversely, there are many hobbyists who view this as strictly a business transaction. Nothing more, nothing less. They put the envelope down, have an hour or two of sex, and walk out. No gifts, no tips; no other compensation other than the required donation. They feel that the best "tip or gift" they can give a provider is a repeat visit.

Thus you are NEVER going to get a consistent answer. Some view tips/gifts as an important element of the entire process; other's feel the donation asked is all the lady is ever going to get. As a hobbyist, its your cash, spend it as you see fit. If you want to get a gift for a lady because she whitelisted you or gave you a reference, I am sure you can E-mail her and explain what you want to do. But make sure its something you WANT to do (because you think its relevant to how you choose to hobby), not something you feel you are OBLIGATED to do. Remember, you have paid the lady for the service she provided and asking the lady to whitelist you or provide a reference is frankly just good business on her part.

It's also important to remember that she is not only offering the reference for your benefit but to another lady in her industry so though she is doing you a favour she is also providing a service to another colleague, her motivation isn't just to assist you but also to provide a valuable service to another lady from whom she may seek a reference from in the future. As a companion I provide references and referrals to other ladies not only as a courtesy to my date but also to other ladies (gents or otherwise identified) in the industry in order to help keep them safe, in turn I ask that when I send out a request for a reference they will respond in kind, with a quick, honest response.
I understand that the reference is important to you and you may wish to thank her for repeatedly going out of her way for providing this information when you request it but it is important to keep in mind that she is also doing so as a courtesy to each individual that works in the industry that relies on this information to keep them safe as well as allow them to better manage their time by focusing on the clients that best suit their interests and services and to avoid those that are not a good match for them.

As was already mentioned if you want to send a gift to someone then that is your prerogative but do so for your own reasons, when she provides a reference she is doing her job and from the sounds of it doing it very well by going above and beyond expectations - perhaps she should be recognized for such as not all companions (or anyone in any industry for that matter) follow through after their engagement is done and that is something that should be valued as well.

I'm sure your generosity would be appreciated but it's not really necessary. Any diligent lady who screens well understands the importance of both giving and asking for references. She may be fielding calls for you and others but she is also calling on other ladies to provide refs for potential clients.  It's a two way street.

As others have pointed out, gifts are never obligatory and your provider has done not only you but herself and the hobby community a service by providing references. Still, if you want to do something special for her, you can either deliver your gift on your next visit or you can send her an e-gift card. For the latter, all you'll need is an e-mail address.