I am not sure how yours is with barking already. Like, does she bark a lot or is already very vocal?
Titan was not.... ever. Lol. So what worked for me was this.. He is EXTREMELY toy driven. I once got him all riled up and ready for a game of fetch. I acted like I was going to through the ball but didn't. It took a little while but eventually he got so excited that he let out a bark (of sorts, lol) and then he got the toy. Eventually he would bark when I held the toy up and I added my speak command "Speak" I would then say that every time I held the toy or my hand up and eventually was able to just say it without the hand being there. I like to teach vocal commands AND hand signals for the same command so I paired the two again with a hand signal of my choice. Consequently, he has 3 commands now for speak, hand over my shoulder (like your throwing a toy), hand on my chest, and "speak."
Commander Charly Titan (GSD)-15 Jan 2010
Lady Athena (BB)-2011-2012 (RIP baby girl)