Eewww bugger, I have a princess too and I'm not sure how she's going to go either...

Anyhoo, if there is tears and screaming I will give her a firm " Byebye, mummys coming back later!" and a big smile and I'll be walking out the door. (maybe sobbing in the car...)
This worked with DD1 an absolute treat, because I always did come back, and because I HAD to go to work. On advice from the staff I snuck back in a few minutes later and she was happily playing on the floor with not a care in the world.

If you let her know you ARE going and if she knows you WILL come back she should get used to it, but if she is a proper princess she will let you know she DOES NOT APPROVE....but it won't kill her iykwim?

GL!