While she's pottying repeat the word that you would like to use as the command to go potty. Praise when she's done. It's really useful to be able to tell them to go sometimes, I do it if I'm meeting a friend for coffee out somewhere and I don't want them needing to go while we're there! Also useful last thing at night when it's cold outside and I just want them to go to the toilet and come in again without conducting their usual border patrol!
That's how I have done it with the last five pups raised. They all understood it after a week. I never praised them; just putting the word and behavior together nd turned it into a habit.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015