If you can, wipe the aTV completely before giving away.
when she plugs it in, she should be given the option to hold her phone next to the aTV, and it will transfer all settings, meaning she should be able to connect to it with the remote app over her own wifi.
The remote app needs a wifi connection to work. devices won't talk directly to each other, so if your wifi isn't around, it won't work.
also, the aTV 4K & HD will both respond to IR commands, any of the old white or silver IR apple remotes will control it.
And a lot of the "many-in-one" remotes have the apple codes built in. You might need the manual to find the code you need to enter on the remote, but there's a chance one of her existing remotes might be able to control it. (don't forget about the cable box remote)