My daughter has insane screaming fits and I don't know what to do about it.

My daughter is 6. Her mother and I split up shortly after she was born, she doesn't remember us ever being together. I have visitation every other weekend.Most of the time she is fine. She's smart, easy to talk to, and rarely needs discipline from me. She's a daddy's girl and we have a very close relationship. The problem is those few times when she does need discipline she winds up having a full blown meltdown.For example, earlier today she was watching tv in the living room. She has a tv in her own room but her brother does not. He wanted to watch tv so I told her she was going to have to move it to her room if she wants to keep watching her show. This is a common thing and normally isn't a problem a lot of the time she'lleven stay in the living room and watch his show with him. This time however she started to argue saying it wasn't fair and didn't want to go to her room. I could tell what was about to happen so I started handling it like I normally do; I calmly told her that I wasn't changing my mind and that if she kept it up she wasn't going to get any tv and would have to go to timeout. She started screaming so I followed through and took her to sit on my bed and told her she'd have to stay there until she calmed down. She kept screaming until her voice literally gave out.I don't spank when she has these fits because nothing helps. Once she starts rolling all we can do is either give in and let her have her way or just ride it out. I do not let her have her way.She does this with her mother as well. One time it happened because she didn't want the eye doctor to put the dilation eye drops in her eyes(the doctor actually kicked her out it was so bad). One time her mother called me to come to Walmart because she had a meltdown over not getting a toy she wanted. It's even happened at school once or twice this school year.I'm personally at my wit's end. These tantrums are getting worse. Her mother tells me she doesn't let her get away with but I know for a fact she will often try to bargain with her or bribe her with new toys to avoid or stop these meltdowns. When I ask her about it she denies it and gets really defensive about her parenting ability.I just don't know what to do any more. via /r/Parenting https://ift.tt/3akWFEJ