Those who discriminate against transgenders (who are by birth as such) are doing wrong and they have their own answering on the day of judgement.
However in regards to a transgender doing haram as you yourself have said, the act is haram and in general it comes with its consequences in the hereafter BUT neither myself nor you can say that this specific person will go to hell because they did this act. We don't know all the details or the conditions of the person committing the act for us to give a verdict. Did the person know what they were doing was wrong? Did they have a choice? What if they have done something good that causes this sin to be cleared of their account? What if towards the end of their life they change and God forgives every wrong they've done?
Hence we can't give a verdict and this is only for Allah to decide given that HE has full knowledge of the person's circumstances and situation.
Furthermore me and you cannot guarantee our going to heaven because we are Muslims then how can we judge or pass judgement on another person's final abode.