I am a LPR. My spouse is in the US. She is working as a graduate assistant at a university and receives monthly stipend. I am planning to file I-130 and I-485 together when visa becomes current in August. However, I am a student as well and my income does not exceed 125% of federal poverty level. I am worried about filing I-864. Do I have to file I-864 along with I-130 and I-485? If yes, will the fact that she is working and earning enough money to sustain herself play any role in the processing of her application?

Yes form I-864 is required document. She can ask others to be co sponsor. Please see this for links: http://www.mygcvisa.com/forum/default.aspx?g=posts&t=1043