It is possible she did mean everything she said, and she did like you as much as it seemed, and that she was caught up in the moment and the "magic"...but once she had left, cooler heads prevailed.

Perhaps she likes you enough that she realises she could be in a position she doesn't want to with you, that if you are only in town for a week giving into her desires would ultimately be bad for her in the end...and because of that is now avoiding you.

Perhaps it is easier for her to just not have contact with you than to feel what she may be feeling but walk away from it for her own good.

I would like to think if I had experience like yours, and that she then didn't seem to want contact with me, I would simply look at it like catching lightning in a bottle, and enjoy the memories of what was.

You don't say if you are married, or how far away you live, or how often you come to Vegas, or any of the other things that might make her reticent to jump into this with both feet...only for a week.  

Her avoidance of you might be an act of self-preservation on her part...allow her that.  You indicate you have called and emailed her, she knows you have tried to contact her, so it is up to her now to decide what she does.  

You mention only this week, and the plans for it...if for you this is just a great time on vacation with a freebie, and hopes for friends and "maybe more" until you go back to your life, understand that for her this might be her life and not a just a vacation fling and let her do what she needs to for her...even if it means hiding from you.