I understand what you are going through (and don't really think the people that are telling you about "tough love" really understand...but anyways...). My brother was treated in a similar manner, getting to live rent free, etc. And my parents do not have the means to support him. Yet they did. They supported him when he kept quitting jobs, quitting school, moving home, move out, quit job, move back in, and over and over. They let him shop in their pantry, they paid for things for him, and on and on. Growing up, he was the headache child. Yet he was allowed to get a drivers license at 16, borrow the car, had insurance paid for, well...you get the picture.
I was the straight A child, never got in trouble (quite seriously never did). Yet I wasn't allowed to get a drivers license til I was 20 (and a year from graduating from college, which I am still paying for), didn't have anything paid for (after high school), etc. My parents did buy me a used car when I went to graduate school.
I guess my parents thought I could handle life and my brother couldn't, I'm not sure. My parents do a lot for me, and I appreciate everything they do (i.e., they helped us move, dogsit for us...). They certainly have done a lot more for my brother (monetarily and other). And it used to eat me up inside when I thought about it; because in reality, I know I'm the one that will be taking care of my parents when the tables turn. And I know that is my responsibility and am more than willing to do it. However, it does leave a sour taste; all the times in high school when my parents couldn't come to my sports games, yet they never missed my brothers. Those are the kinds of things that bother me more than the monetary issues.
I've learned to just deal with it, but it's not easy to feel like you did something wrong, or you aren't good enough to get the same treatment as a sibling. When it comes down to it, I guess it's good to be the one that was able to support themselves, and the one that family can depend on down the road. It's still hard to deal with the feelings of jealousy sometimes though, and you aren't in the wrong for feeling like that. I'm sure a lot of people do. We all just have to learn how to deal with it, and realize that in the end, we do have it better. We aren't dependent on other people.
Unfortunately, my husband and I are in the same situation (his sister has mooched of his parents for so very long...and we will be the ones to take care of his parents when the time comes, as we've already been told that his mom expects to move in with us in the future). It's funny how it works...we are lucky to get one visit a year from his mom (his stepdad doesn't even bother to come); we get small token Christmas gifts, no phone calls, etc.). His sister gets help with bills and rent, computers, extra money, many visits (from both her mom and stepdad), etc. but we are going to have to make provisions for his mom to live with us, since that's what was told is expected of us. We'd never turn her away, but it's hard that my husband doesn't get to spend time with his mom now; we're not concerned with the monetary side. (And before anyone asks...there's been too many times we've gone there to visit and she's only been able to spend a hour or so with us (over the course of a several day visit) because she has better things to do, and I'm not talking about working).
My long, drawn out point is that you are allowed to be upset about it. Don't let anyone make you feel bad for feeling bad. You just have to come to realize, in time, that you are better off. She is probably secretly jealous of you for your independent life (though I'm sure she'd never admit it).