I need help with for TP-Link Router

Model: TL- WR841ND

I'm currently using UniFi with 20mbs. How do I set up the QOS for this? I'm trying to limit my sister to 5mbs because she streams and dl her korean drama at the same time while I'm paying for the bill.

I tried doing it by setting the IP of her comp and my comp.

Sis
Upload 0-500kbs
Download 0-500kbs

Problem is that It's not working and when I enable the QOS, my upload drops to 5mbs while download still remain at maximum speed.

Doing this over wireless? Or it only works on LAN?