Turning the tables:

She can come and go as she pleases because she is a poor earner and will probably get bounced eventually. So management attitude is probably non-confrontational: "Why start some shit with her when we're just going to can her soon anyway."

Whereas you're a strong asset management wants to continue developing / earning from. So when you want the same life as your coworker, management is probably thinking "Shit, we hope you don't turn into her - we are gonna bounce her ass. Don't go down that path, keep doing what you're doing because that's why we value you."

The real problem isn't that youre not able to enjoy the lifestyle of your peer. Rather, your spineless management is letting it slide with a poor performer and thats setting a bad expectation for other workers (like you).

Keep in mind I'm a Redditor and have little context on the work environment of your industry.