To recap: using the native #Discord client on #macOS, each time my partner opens a stream, her #MacBook Air would slow to a crawl or even crash entirely, and she'd need to reboot and just no longer able to watch the stream, other than to switch to her PC.
The (shocking) solution: on her MacBook, use Discord through #Firefox instead. I doubt that it needs to be Firefox, perhaps #Safari would do too, but she used Discord on Firefox and her Mac's able to watch streams on Discord just fine now. She even said she's never experienced Discord this smoothly on her Mac before lol so if anyone has had any issues with Discord on their Mac recently, maybe try using the web client instead.