need advice for a friend! : update 1

Okay so I know how this sounds. But this is a legitimate story. My friend got pregnant by her step-dad. Her mom is also pregnant by him . I asked her if he raped her and she admitted that she WILLINGLY slept with him. I know. Completely wrong to do that to her mother despite the struggling relationship she has with her. Now my friend doesn't want an abortion, but wants advice. I am so confused and don't know what to say. Any advice? Put as annon. Because this is a serious and sensitive matter. Just looking for some great advice from other women. 
Update one: she has talked to her step dad and he denied it being his. She told her mom and her poor mom is so confused and doesn't know who to believe. I should clarify that her mom knew she was pregnant but she didn't know the dad was. But since it is my friends 5th month and her moms 6th she knew that it was closing In on it all coming out anyway. I didn't even know it was his until a few days ago . I will update soon. And those wondering my friend is 20 years old