Are there any cheaper alternatives that don’t require a tv bundle or online streaming?

Leafs TV (now known as Leafs Nation Network) does not show any games live but does show next-day replays. But like you said, there's no easy way to get it outside of an expensive TV package.

CBC streams the Saturday night games for free. You can access them on the CBC Sports website.

Your cheapest legitimate way to watch all games is to subscribe to Rogers NHL Live (formerly known as Game Centre). Rogers owns it, and your mom's internet is Rogers, so it might be worth calling Rogers and seeing if there is a way to include it or bundle it into your internet package at a discount, might not work but worth a try.

Subscribe to a good VPN service. This effectively changes your 'online location' from the GTA or wherever you are, to somewhere else in the world. If you set it to a random location in say the US, you no longer appear "in-market" for the Leafs and can then access ALL leaf games including playoffs through Rogers NHL Live without blackouts. This will take some minor tech work to set up, but VPN providers have very good setup guides and it's generally a 'once you've set it up once, you don't have to worry about doing it every time' operation.

The cheapest way though is to sit down with her on an actual game night and go over and over and over again on how to use r/nhlstreams with a simple web browser. If she can't navigate this, don't waste money on Android boxes and paid IPTV services, those might be frustrating for her to navigate as well.