Is it proper etiquette to order her drink and entree before she arrives?
Proper etiquette dictates that you treat your date with consideration and respect.
Etiquette also dictates that your date be poised enough that she doesn't need to gulp down a drink as soon as she arrives. It could be insulting to imply otherwise.
An enjoyable part of a dinner date is often the chatting over an aperitif, commenting on the menu, getting acquainted while sharing little stories about what each of you like and don't like. Dating etiquette doesn't demand that you both have a good time, but dating etiquette would be happy if you did.
If the restaurant is busy and you are trying to expedite matters for everyone's convenience, your concern is misplaced, as it should be solely on the comfort and enjoyment of your date.
Finally, the age has passed where men treated their dates with benign but dictatorial guidance, or like fragile and somewhat dim princesses whose decisions may not be as informed as your own.
In other words, be happy to see your date when she arrives, smile, relax, listen to her, take your time, and enjoy!