I would get her a Roku, they're simple and amazing. Not sure about Chromecast or the Amazon tv thing but I've had a Roku for a few years now and it's the best, has a ton of apps too like Pandora and the remote only has a few buttons. It's wireless and both AV and HD compatable.
The Roku 2 is about $60 so you may be able to find the first one. The 3 is $100 so I'm sure that's a no but the USB stick is only $50 but you have to have the port on your tv.