how do i convince my mom to stop taking me to the therapist when im tired or sick ?

how do i convince my mom to stop taking me to the therapist when im tired or sick ? hey there, im 15, i go to a therapist but sometimes i get really tired or sick and my mom still takes me to the therapist even though he told me twice to never go to him while im tired cause i become unable to get the words out. i told her so many times (the therapist did too) but she just keeps ignoring me and say "you just don't wanna leave that damn computer" cause im a gamer, and everytime that happen we go there, i fail to get the words out even though i always do what the therapist say and i become able to talk normally, the therapist tells her that i didn't do well, she gets mad at me and tells me that she'll take my computer away if i didn't get better. im so mad and tired because of her ignorance, and i just can't do anything about it cause she interrupts me whenever i try to talk to her then leave before i finish talking.