Its tough, and you are doing a great thing. I think your sister had a hard time, being separated with baby's father etc. But you know, it sounds like she just takes all you do for her for granted. I agree she's immature, but what if she "matures" when she reaches 30 years old? Until that time you gonna be babysitting HER and not being able just to study for college and get a job? I think you should talk to your parents, and honestly, since they buy baby stuff and she just wastes that money, I think she will be able to afford a babysitter. As you said, don't get sucked in that hole.