10 mo old niece hates napping alone

Hello everyone, I have a niece whom I have been watching for the past 7 months, about 4 months ago I have tried to start sleep training her to sleep by herself. I have another niece who I will start watching by May/June time she will be around 3 mos old..

I have tried the Ferber method but since it is so inconsistent with being at my house versus her own it hasn’t been working. Lord knows I love my cousin (nieces mom) but she still sleeps with her at night and for naps. I am now trying the CIO method. Boo me all you want, I did it with my daughter and she turned out more than fine with her school scores higher than the schools districts average.

I have asked my cousin to please try to get her to sleep by herself but I guess you can say she doesn’t have the patience. And when my other cousins watch my niece they hold her to have her fall asleep too. It just seems like I have no support and I need her to start falling asleep by herself especially before the new baby comes.

I watch her 4 times a week and am currently my third day of CIO method, I have done some research and saw you can let them cry for 30-60 minutes and since I know how stubborn she is I let her go for 60 minutes. If she can’t fall asleep we get up and get lunch together and eat. And I keep her up until 2:45 so I can go wait in the pickup line for my daughter and my niece could sleep in the car. What more can I do?