Why should she have to take care of her older sister?

When should family help family? There’s a huge difference between helping your elderly mother, who genuinely needs outside help to function, and enabling young, healthy family members who don’t need as much help as they claim they do. If you have a kind heart, you might feel you should help anyone who asks, but that can hurt you in the end. Enablers are the nicest people on the planet, and they feel like they’re doing something right by helping someone who keeps refusing to help themselves. 

If you’re going to let a family member live under your roof and pay a reduced rent price, you need to have a serious conversation about your expectations of their stay before you agree to it. Are you okay with them staying for a month? A year? Are you willing to house them for as long as it takes them to «get back on their feet,» because that could take years if you let them stay rent-free? Are they allowed to eat your groceries? Are they expected to help around the house? If you don’t set clear expectations and hold your guest to them, there’s a good chance they’ll take advantage of your kindness for as long as they can. 

The young woman in this story has let her older sister walk all over her for far too long, and it’s time that she grows a backbone and tells her that she’s not going to subsidize her life any longer.