I would ask the dog's owner if she knows whether there was something you were doing that might have triggered the growling, so you could avoid doing that next time. Or if there's anything you can do to let the dog know you are a friend, like give him a treat.

Ultimately, his good behavior is his owner's responsibility, but as long as you need to be going into that space, it might be helpful to talk about how you can get along with the dog. Maybe invite her to bring him to your part of the office for a visit, so he can get to know you in a different setting. Get creative!

It took us a while to figure out Gordy's triggers when we first got him. He doesn't like fists, but the first time someone held out a closed hand for him to sniff as a greeting, we didn't know that. And it took several instances with different people for us to notice a pattern.

It also took us a while to figure out that the more a new person tries to engage with him, the more uneasy he feels. He always gets ramped up when people come to the door. Now when people come over, we have them give him a treat at the door, and then tell them not to interact with him. No petting, no eye contact, no talking to him. He calms down a lot faster that way, and half an hour later he will be totally unconcerned about the new person. Sometimes he will even cuddle up to them.

Don't know why he is like that, but dogs can be funny that way.