Disappontment - Dinah

Last night was trying to revise Dinah's math, as well to reinforce her addition and subtraction. I know she's having problem with that.
I started off with simple addition before I progress to bigger number. Initially was fine, gradually as the number become bigger, she become nervous and forget even basic addition like 2+1.
I tried to guide her back on track, but seems like nothing can get in. I tried to contain my disappointment. I teach her many time, and once I stop, she forgets everything.
It's inexcusable to say she doesn't knows 2+1, so I took out her piggy bank, her favorite stuff. Only when she sees her stuffs being confiscated by me, then memory flood back.
She was doing fine, when she slipped again. This round, I'm frustrated, so I want her to sleep at her own room. She's not sleeping with me.
She cried for quite sometime, but I already told her if she doesn't concentrate, then she will sleep her own room. She needs to learn that my words are not to taken lightly. She must starts learning to finish her works before she can plays.
It's good to set her routine, else she might plays non-stop, and neglect her works.