LMG - well, ideally you should be taking her to the potty so she begins to understand the whole process, rather than 'catching' the wee.
BUT, if she does do a wee in the potty then give her lots of praise.
And then take her to the potty in another half hour or so. You have to take them to the potty/toilet in the early stages, then a bit later you can progress to looking out for the signs (dancing around etc).
Good luck!
I'm waiting for today's poo - no sign yet!