My sister asked me to be the guardian of my niece if something were to happen to her and her boyfriend. I don't know the process of how to get this done. I'm 27 and single with a steady income. Do things like that play a factor as well.

She can make you a 'testamentary guardian' in her will, setting up a trust that will allow you to make financial decisions concerning trust property; or she could appoint you a temporary guardian while your niece is in you care. Check this: Choose Legal Guardian - Choose Legal Guardian for Your Children