Thanks to Sm1smom and aos13 for your answers. I doubted that too when I heard him advise my sister to apply for EAD right after DSP-122. I do have some more questions regarding my sister's case:
1. She went to a university just to get an advanced graduate degree, but after one semester, she felt that she needed to improve her English and have her I-20 transferred to a language school. She has now been in a language school for two years. Does that pose a problem for the interview?
F1 is F1, I don't think her status would be a problem, but I don't know for sure.
2. She has not been paid but rely on family fund for her school. So based on your answer, she will need to have a USC to sponsor her. Is that correct? Can she use affidavit of support from family in home country for AOS?
USC or LPR. Or she can have money transferred to her account here in US and show that.
3. What kinds of responsibilities that a USC sponsor will have to bear? and in what circumstances? If she chooses to go on a CP route instead, will she need a USC sponsor as well?
If she needs a sponsor, regardless of CP or AOS she'll need a sponsor. But, in CP one can show things like property (house, car, etc.) in one's name which would be hard to do in AOS since IO would have no idea about some property in some foreign country. Her sponsor would be responsible if she ever uses public assistance.
4. I read a post somewhere above asking including parents' name. Is it possible that a selectee's parents be included in the application? Our parent is at home country, so if it's possible, my sister should instead consider CP?
Parents' names will be in application forms as information, they won't be called to interview or get a green card.
Thank you!