NEED ADVICE!!! Please I'm torn!!

Ok about a year ago my sister, who has 3 kids decided to leave her children's father n marry an old boyfriend who is on drugs and just no good on many levels!! She started doing drugs, abandoned her kids & left all 3 w/ me. Girl is 13, boy 10 & boy 2. At first I had all 3, including my own. I soon realized it was to much for me, so the 2 boys went with dad, I kept my neice. Who cuts herself, is extremely depressed, lazy, doesn't help me at all & disrespectful!!Not to mention jealous of my daughter. She gave me anxiety say the least.I had her for 9 mnths then finally had her go w/ her dad. Bc I couldn't take anymore..She "hates" him n in some way he neglects his kids.. Just a deadbeat!! Yes CPS is involved. She wants to come back with me, & my father is forcing me to take her. Against my better judgement I said yes. I really don't know wat to do bc I love her, but she's troubled!! I feel guilty having her w/ her dad who really is a loser. Her mom is not complying w/ CPS. So this could be a long time!! Not to mention i just found out I'm pregnant!! I'm torn, any advice on what I should do?? 2nd chance or no way???