Honestly I would be upset too, I'm upset for you just reading your post! While it's true nobody "owns" names, I think, given the situation and your conversation with her, that what she did was really, well, disrespectful, insensitive, and just plain not okay. That being said, it's the name you had already chosen for your baby, the name that feels right to you, and I don't think you should feel like you have to choose a different one. The name you choose will be with your daughter for the rest of her life, but I doubt you will be working with this woman for the rest of yours, and after this I doubt you'll be socializing much outside of work. I say keep the name, and if someone asks, you can simply tell them the truth: you had chosen the name and told your coworker, then she decided she liked it so much she used it too. Best of luck with whatever you decide!
Use the name anyway!! Don't give up on the name because of this. It was an awful thing for her to do, but others are right, you probably won't work with her forever and your daughters will probably never meet. And if anyone from work comments on it, you have the chance to be honest about what happened and they will probably agree it was a dick move on her part.
I had a similar experience, but my husband reminded me that they are not family and most likely won't be in our lives a couple years down the road. If you are 100% happy with that name, then I say use it. Your co-worker will get over it, and she is just a current co-worker not family.
Re: stolen baby name
Or name her same name anyway. but put princess at the beginning hahaaaa