AITA for telling my niece that she has no idea how hard my life is and to stop complaining about her husband not satisfying her sexually?

So this did happen over Christmas and I (38m) was over my sister's (39f) place with my wife (39f), my son (9m) and my niece (14f). For context my sister's family is very well off, they live in a mansion, she has a husband that caters to her every need, their two daughters (including my niece) are almighty and go to the very best school in the area, have ever had everying they have ever wanted, and are spoiled brats.<br><br>So me and my wife were sitting with my niece talking and she starts to complain about her husband not giving her enough attention in the bedroom and how she has to tell him like 5 times to make sure he doesnt forget. She then goes on to say that he is not the best at it and that she misses the pleasure she gets from having sex by a past boyfriend. My wife then told her that she has no idea how hard my and her life is and that she should be grateful with what she has. I then backpedaled and tried to smooth the situation out but my niece got upset and left the room crying.<br><br>My sister and her daughter went up to me after and told me that I was a heartless asshole and that while my niece may have it good, she doesn't know what it is like to have a shitload of pressure on you. I then again said that she had no idea what my life was like, because she has never worked a hard day in her life. My sister lost it at this and told my kid to get out and not never come back.