Make sure you take a video (on your phone even) of unpacking the box. If the snake were to arrive dead that's your evidence to get a refund from the seller, or at least to prove that you actually got a dead snake and arn't out to get a freebie.
Check her over closely for mites and anything unusual as you'll want to bring this to the attention of the seller if need be.
There's a great thread/sticky on here all about QT, I'd look it up (I tried but couldn't find it for you lol)
And let her settle in as with any new addition, perhaps wait a week to try to feed though I've tried the day after with receiveing snakes and they took their food fine. Keep an eye out for any weirdness in the QT period.
Congrats on the new addition!