Yeah, uhm, I want to point out that yes, this is not a good way of calling a transsexual. But that woman might not be saying it in a mean way. Maybe she thinks it's a respectful way of calling a transsexual. In that case, she needs to be educated, not yelled at or reported. Some people just never learned some things that seem obvious otherwise, or learned it wrong. And it's often impossible for them to just figure out that it's not okay.
If you took a woman from 1950 and teleported her here, even if she were very sympathetic to Blacks, she might still call them ->-bleeped-<-s. Getting all angry at her wouldn't be appropriate. You'd need to teach her those things. It's the same for people who were educated wrong. They don't know otherwise, so leave them a chance to correct themselves.
Of course, if after a good explanation she insists on calling it that way, then yes, you can regard it as a proper insult and act accordingly. But doing so before such an attempt is premature and even disrespectful in a way, if you ask me. Sort of like punishing a child for eating your cookies whilst they didn't know they couldn't eat it.