Through a decent telescope, Jupiter looks like a mini solar system. You can see its bands and four biggest moons, which is wild for something so far away. Your sister probably gets hooked on that moment of clarity when everything snaps into focus. I borrowed a scope once and stayed out until sunrise (my coffee bill was brutal the next day). It's easy to lose track of time when you're seeing something that real.
That "coffee bill was brutal" line is the real truth right there. You pay for the telescope once, but you keep paying for the hobby every morning after with those giant coffees. It's like a subscription fee for the universe. Your sister is basically trading sleep for gas giant views and then trading cash for caffeine to function. I guess some people just really need to see those moons more than they need to see their bank account.