Lots of my Gay friends who are friend with TS girls, they keep using it, from what I see, people use the word Tranny when they are being provocative and use it as an insult similar to F word N word, it seem OK if you are in that community, but not ok for anyone else. Maybe depend on how, who say it.

Transvestite also derogatory word use in Latin America.

The appropriate term would be Transgender, Trans Girl, or just simply TS Girl.

Also the word CIS ( cisgender ) is a new term which I'm still studying it, I still don't get it.
Cisgender is Essentially the opposite of transgender; whereas transgender people are those whose gender and assigned sex at birth don't match up, cisgender people are those whose gender and assigned sex at birth are the same.

Hope that help!

my  opinion

being open minded words are words they are meaningless unless they are put in to good words or words that is use into action to demean or degrade person

She
 

If you absolutely have to specify what kind of lady they are, 'trans woman/lady/girl' is pretty much a safe bet, the same way you'd use any other adjective  

Language is constantly changing and not even consistent, especially when it comes to gender and sex. Just look at the way "gay" or "queer" has changed over the decades. I'm not sure if there is one term that's always OK all the time. I think the key is just to be mindful and respectful.

"Tranny" can be very patronizing and objectifying especially when used flippantly, but not everyone finds it offensive. Sometimes I use it to refer to myself or a friend in an affectionate sort of way. But I'm a tranny. Like Asian-Gee said: along the same lines as the F-word or the N-word, unless you're a 'tranny' yourself, you probably shouldn't just throw the word around.

I like the sound of the word.  I've been with multiple providers who referred to themselves as a tranny or their cock as a tranny cock while talking dirty.  I wish it wasn't considered derogatory.

i think it is at least for me and some other girls i know best word is a tgirl  
if you call her tranny then you should be ok with others calling you tranny chaser