Recognize that the channels you install are tied to your ACCOUNT, not to individual devices. Add a channel to one, you add it to all channels on the account. Delete from one, delete from all.
Your s.i.l. might be better off with her own account at Roku.com so she can control her channel selection separately from yours. There is no charge for setting up a Roku account. Do a factory reset on the unit so you can set it up for the new account.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Do not ask me support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking "Accept as Solution.". Please only do this if it ACTUALLY solves your problem.
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X | Streaming Stick 3600