The Roku can only be controlled with a Roku remote. The TV remote will not control it (a few TVs will pass a few commands through to the Roku, but in general that's not the case). Depending on the model Roku you gave her, you may need an official Roku remote. If it is a Roku Stick (that plugs into the TV without using an HDMI cable) then you must have a Roku Voice Remote, as the Stick will only work with a WiFi Direct remote.
If it's any other Roku player that uses an HDMI cable, then you can use either the Roku basic remote or a generic universal IR remote that has the codes for Roku players. Those can be found in any store that sells remotes, sometimes for less than $10.
As to the account, unless you want her to have access to your account, she should create her own Roku user account (it's free). Then she can install whatever apps she wants to use without impacting your Roku. If both are linked to your account, she can add and remove apps from her device and they will be added/removed from yours. So it's best she has her own account.
To move the Roku onto a new user account, the Roku needs a factory reset and set up again like it was new. There's no way to transfer a Roku from one user account to another without wiping the device.
Dan
Roku Community Streaming Expert
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