HELP with Toddler!!!! Not my kid

My parents have been taking care of my cousin’s daughter. My cousin was an orphan, my parents met her when she was jobless, pregnant, and just got out from the relationship with her baby daddy. My parents take care of my cousin like her own daughter and take care of my cousin’s daughter too since day one. My niece is 16months 😬 she basically goes back on forth to live with her mom and my parents.

I come to visit my parents, since I’m around my niece stay with me and my parents. Her mom is not working, dating two men as sugar baby and I just found out she started using drugs again since she was dating one of these guy.

My parents are so busy lately so im babysitting my niece, I suppose to take my her back to her mom but finding out she’s been drinking and using drugs for these couple days. I just can’t take my niece back to my cousin😭 I already told her that I don’t agree with her lifestyle choice, She deserves to be happy and live her life but there’s a child involved now. I don’t like the dating thing too because this kid never met her dad and constantly meeting these two men her mom dating😭 We tried to talk to her about my parents adopting my niece but my cousin refuse because she can’t be separated with her daughter. My cousin had a rough life but I wish she learned from that and see that kid need more than her mother giving birth to her😭

I’ve been taking care of this kid for almost a week now and I still have no clue how to do it right😭 she doesn’t want to eat her food, I tried to change the menu all the time. She only want to drink her formula that I’m strictly not giving her more than 3times/day. Getting her to sleep is really hard OMG I have to let her watch videos on youtube for couple hours 😭 and I can’t poop alone😭 she will scream and look around for me😭 I feel so bad but I don’t want to get her back to my cousin before she get sober for couple days😭

What should I do to make her eat? She spits out all the veggies I gave her too😭

My mom is not coming home for another week and my niece keep crying for my mom at night 😵