How do I politely address you??!!

I am so sorry if I offend anyone with this topic. I promise that is not my intention. If you are just looking to argue and just pretend to be offended to start a fight then this post is not for you. This is a matter of how to be respectful.

Okay. There is a person. Who is working with me. I am not being rude. I can see by looking at this person physically that this person was born a female. Has female characteristics like breasts and uses the girl washroom sounds like a female and even has a female name. (I'm using a fake name of course but it is a typical female name such as Amy or Hannah or Rachel...not a unisex name for instance like Alex would be) But the only thing that this person has said is "I'm not a girl so don't refer to me as one". This wasn't said to me directly. This is what they announced.

This person has never said please call me this instead.

I'm worried because I dont want to accidentally address this person the wrong way. What do I say? I want to be polite and respect whatever this person's wishes are.