I'm not going to help my sister with a job application.
Why don't you want to help your sister with an application?
I think she should do it by herself.
You should consider helping your sister with the application. Sometimes people aren't able to do everything by themselves, so giving them a hand is a good thing.
What about a job is so important?
Helping your sister with the application will help her to get a job and be more financially responsible. If you do this she will be more likely to help you in the future.