Step sister getting a free ride

So me and my boyfriend live with my dad. We pay rent we pay our own bills. He was working full time but was recently laid off so he’s looking for a job now. Im a full time student. I’m expected to pay for everything myself and get 0 help from my parents whatever i honestly have no problem with that what i do have a problem with is my step sister getting a free ride. She is a year older than me but dropped out of high school during her sophomore year since then she’s has one job for 3 months 2 years ago and nothing since. She sleeps everyday till 4-5pm doesn’t shower doesn’t clean up after herself and uses all my stuff. I literally have to hide toilet paper from her or she will use all of it because i buy the nicer toilet paper compared to her mom. What really pisses me off is that she gets an allowance every month. She does nothing. She doesn’t pay a single bill or rent nothing doesn’t work sleeps all day but gets allowance. I’m just as much my fathers daughter so why am i expected to do everything myself when she isn’t? I’m struggling to get stuff for school but my step moms already said if we are even a day late on rent we get kicked out within 24 hours. How is this even fair??

Edit: as my step mom said she’s going a a big trip in 2 weeks for a month. And guess who’s paying for everything? Not my step sister. My dad knows how tight money is for me right now and said nothing. My step mom said my rent money goes to my sister. So I’m paying for her trip.